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PubMed1981

Effect of manipulating central catecholamines on puberty and the surge of luteinizing hormone and gonadotropin releasing hormone induced by pregnant mare serum gonadotropin in female rats.

We have investigated the effect of manipulating central catecholamines on the timing of puberty (as assessed by vaginal opening) in female rats and the surge of luteinizing hormone (LH) and gonadotropin releasing hormone (GnRH) induced by pregnant mare serum gonadotropin (PMSG) in immature female rats. Manipulation of the catecholamines was carried out with either 6-hydroxydopamine (6-OHDA) administered with or without either desipramine (DMI) or pargyline, or alpha-methyl-p-tyrosine (alpha-MPT). The neonatal administration of 6-OHDA delayed puberty, an effect which was potentiated by pretreatment with DMI and was associated with a reduction in the rate of body growth. Catecholamine fluorescence in animals aged 60--65 days that had been treated with DMI followed by 6-OHDA was diminished only in the caudatus--putamen; treatment with 6-OHDA alone resulted in diminished fluorescence in the hypothalamus and in the intermediate but not the external layer of the median eminence. The neonatal administration of alpha-MPT had no significant effect on either the growth rate or the timing of puberty. Regular oestrous cycle occurred after puberty in animals treated with either 6-OHDA or alpha-MPT. The PMSG-induced LH surge was significantly enhanced by 6-OHDA (administered i.v.) plus DMI, and reduced by 6-OHDA injected in to the lateral ventricle (v). The inhibitory effect of 6-OHDA (v) was reduced by DMI, but in animals given 6-OHDA (i.v.) after pargyline there was a marked reduction in the height of the LH surge. There was a good correlation between the changes in the concentrations of LH in peripheral plasma and the concentrations of GnRH in pituitary stalk plasma in that the PMSG-induced surge of GnRH was significantly increased by 6-OHDA (i.v.) plus DMI and reduced by 6-OHDA (v). In animals treated with 6-OHDA (i.v. plus DMI catecholamine fluorescence was reduced only in the external layer of the median eminence, while after 6-OHDA (v) plus DMI degeneration was seen in the medial forebrain bundle. These results demonstrate a marked difference between the long-term and acute effects of 6-OHDA on the gonadotropin control system. Neonatal treatment with 6-OHDA plus DMI significantly delays puberty and the rate of body growth, but does not affect cyclical gonadotropin release and has no persistent effect on the hypothalamic catecholaminergic systems. The acute administration of 6-OHDA, depending upon the route of administration and whether it is given after DMI, can either potentiate or inhibit the PMSG-induced surge of GnRH and consequently LH by mechanisms which involve destruction, respectively, of either dopaminergic terminals in the median eminence or catecholaminergic fibres in the dorsal hypothalamus.

Animals↗
PubMedDate not supplied

Puberty and early sexual development in Libyan fat-tailed ram lambs.

Puberty and early sexual development were studied in 143 Libyan fat-tailed ram lambs, equally representing Brownhead and Blackhead strains of this breed. The two strains did not differ in any of the measured parameters in a consistent way, yet the Brownhead lambs tended to be slightly heavier and to have a slightly larger testis diameter than Blackheads. At the commencement of the observations when the lambs were 69 days old, 25.2% had fully descended testes at a significantly higher (P less than 0.01) mean (SD) body weight (24.1 +/- 4.1 kg) than those with partly descended (69.2%, 15.7 +/- 6.3 kg) or with non-descended testes (5.6%, 19.5 +/- 3.2 kg). Testes development followed a triphasic pattern with an initial and a final phase of slow growth and a middle phase of fast growth, commencing at a weight of 24.5 kg and an age of 85 days and lasting until the weight of 36-43 kg and age of 180-200 days in both strains. The separation of penile adhesions commenced at a mean body weight and age of 33.6 +/- 3.7 kg and 125.5 +/- 27.4 days respectively and was completed at a mean weight and age of 38.3 +/- 4.2 kg and 153.4 +/- 29.9 days. Only four lambs failed to show complete penile separation. Age had little influence on testis descent or on penile development. Puberty was assessed in 71 lambs using sperm recovery following electroejaculation as an end point. Most of these lambs (92.9%) reached puberty at a mean (SD) age of 171.5 (39.9) days, mean body weight of 39.9 (9.3) kg, mean testis diameter of 4.1 (0.4) cm and mean horn length of 21.4 (3.7) cm. Puberal lambs were significantly superior to non-puberal lambs (P less than 0.01) in all these counts except for age which was similar in both categories. Direct testicular observation showed a strong correlation between testis diameter, testis weight, body weight, sperm concentration/g testis weight and to testis histology. Age was poorly correlated to testis weight, histology or sperm concentration. It is concluded that the body weight is a major determinant of puberty in this breed. It is also considered that the two strains of the breed are remarkably similar in the studied aspects of puberty and sexual development.

Animals↗
PubMed1981

Delayed puberty in gilts in total confinement.

Two hundred fourteen crossbred gilts, born in January through March and June through July of two different years, were raised in total confinement until 100 to 120 days of age and then moved to an outside dirt lot (non-confined) or to a single pen in a confinement, finishing building (confined). Beginning at 150 days of age, estrus was checked daily with a boar to determine percentage of gilts that attained puberty and age at first estrus, and weekly blood samples were collected and analyzed for progesterone by radioimmunoassay to determine age at first ovulation. In the Jan.-Mar. born gilts, 75.4% of the non-confined gilts and 37.4% of the confined gilts attained puberty by 270 days of age (P<.001). Although differences were not significant in the gilts born in June-July, more non-confined gilts (62.6%) than confined gilts (50.9%) attained puberty. Of the 121 gilts that ovulated, only 1 non-confined and 3 confined gilts did not exhibit estrus. Average age at first estrus or at first ovulation were similar for confined and non-confined gilts. Adrenal gland weights at 250 to 270 days of age were similar also for confined and non-confined gilts. Based on the results of this study, we conclude that total confinement housing can reduce, by as much as 50%, the proportion of gilts that attain puberty by 8 to 9 months of age and that time of year may influence the extent of delayed puberty.

Journal Article↗
PubMed1982

Effect of level of nutrition on onset of puberty and conception rates of zebu heifers.

Sixty zebu heifers were divided into three equal groups and reared on isocaloric diets but on different levels of protein. The protein levels were 19.17% (high), 13.37% (medium; NRC recommendations) and 8.3% (low). All animals were examined weekly per rectum for the presence of follicles and corpora lutea and also checked daily for standing heat. The presence of a mature corpus luteum was considered to indicate the attainment of puberty. Body weight and pelvic dimensions were taken at biweekly intervals. Intact bulls were introduced to heifers after they reached puberty and once they reached 200 kg live weight. Pregnancy diagnosis was carried out at 60, 90 and 120 days following introduction of bulls. Mean age at puberty for heifers in the high protein group (570.4 days), medium protein group (640.8 days) and low protein group (704.2 days) differed significantly (P<0.05). body weight at puberty for heifers in the high, medium and low protein groups was 207.1, 187.0 and 161.7 kg, respectively (P<0.05). Pelvic size at puberty was not influenced by the nutritional level. Conception rates of heifers in the three groups were influenced by level of nutrition. Pregnancy rates for the high protein group (58.8%), medium protein group (27.8%), and low protein group (16.7%) by 90-day post-breeding period were significantly different (P<0.05), but body weight at conception between the groups did not differ significantly. The results show that increasing the protein level in the diet is a means of improving the reproductive performance of zebu cattle.

Journal Article↗
PubMed1987

The effect of protein intake on the onset of puberty in Bunaji and Friesian x Bunaji crossbred bulls in Nigeria.

Twenty-one Bunaji (BJ) bulls and 21 Friesian x Bunaji (FRxBJ) crossbred bulls, approximately 6 mo of age were divided after weaning into two groups and fed isocaloric rations (2.40 ME Mcal/Kg/DM) containing crude protein levels of 14.45% (high protein) and 8.51% (low protein) for a period of 16 mo to determine the effect of protein intake on puberty. Animals on high protein diets ejaculated first motile spermatozoa and attained puberty at significantly (P < 0.05) earlier ages than those on low protein diets. Mean ages at puberty in mo for BJ on low and high protein diets were 15.50 +/- 0.51 and 14.82 +/- 0.68 and for FRxBJ, the ages were 17.79 +/- 0.82 and 12.94 +/- 0.60, respectively. The animals on high protein diets at point of puberty had significantly (P < 0.05) lighter body weights, smaller scrotal circumference, lower chest girth, better body condition score and better sperm quality than those on low protein. There were no significant (P > 0.05) differences in withers height or volume of semen at puberty for the two protein diets.

Journal Article↗
PubMed1989

Effects of rapid weight gain to puberty on reproduction, mammary development and lactation in ewe lambs.

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P<0.05) but required more services per conception (1.3 vs 1.1, P<0.05). Dietary conception rate and lambing rate means were similar. Mean 4-h milk yield was lower (P<0.10) for ewes on the finishing diet (283 g) than for those on the growing diet (310 g). Mammary gland fat pad area was higher (P<0.05) for ewes on the finishing diet compared with those fed for growth. Gross and adjusted duct areas were higher in ewes on the growing diet, but differences were not significant. At puberty, negative correlation coefficients for milk yield with performance traits were as follows: daily weight gain, -0.184 (P<0.08); weight-to-height ratio -0.262 (P<0.01); body condition score, -0.189 (P<0.07); and body weight, -0.212 (P<0.05). Results of this study indicate that rapid weight gain to puberty impairs mammary gland development and milk production in ewe lambs.

Journal Article↗
PubMed1992

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran x Friesian heifers in Ethiopia.

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.

Journal Article↗
PubMed1992

Relationship of testicular growth and size to age, body weight and onset of puberty in Menz ram lambs.

Scrotal circumference as an index of testes size, along with body weight, wither height, heart girth and body condition score were measured fortnightly for 114 Menz ram lambs from weaning (91+/-7 SD days) until puberty, which was defined as age at first collection of an ejaculate with 50 x 10(6) spermatozoa and 10% motility. The animals were maintained on poor (n=28), low (n=29), medium (n=29) or high (n=28) levels of nutrition through grazing and supplementation. Further, half the lambs in each group were drenched for endoparasites. Daily gains in live weight, wither height, heart girth and scrotal circumference were 48.5+/-1.6 g, 0.05+/-0.01 cm, 0.07+/-0.01 cm and 0.07+/-0.03 cm, respectively for the period from weaning to puberty and varied with level of nutrition (P<0.05 to 0.001) but not with drenching or its interaction with nutrition level (P>0.10). Scrotal circumference increased linearly and was strongly correlated with age, body weight, wither height, and heart girth (r = 0.83 to 0.85, P<0.001), and lamb weight could be predicted by the equation: 6.35 + 0.53 scrotal circumference (R(2) = 0.73). Mean age, body weight and condition score at puberty were 288+/-6 days, 19.3+/-0.4 kg and 2.6+/-0.06, respectively, and varied due to season of birth, level of nutrition and weaning weight (P<0.01 to 0.001). The nutrition level also influenced (P<0.001) scrotal circumference at puberty, averaging 21.5+/-0.3 cm. It was concluded that postweaning nutrition management had a strong influence on lamb weight gain, which in turn was related to testicular growth and puberty onset in Menz ram lambs. The suitability of scrotal size measurement as a criterion for early selection of tropical ram lambs is emphasised.

Journal Article↗
PubMed1995

Differences in early patterns of gonadotrophin secretion between early and late maturing bulls, and changes in semen characteristics at puberty.

In prepubertal bull calves there is an early transient rise in gonadotrophin secretion between 10 and 20 wk of age, and it has been suggested that this plays a role in the attainment of sexual maturation. To test this, we looked for differences in the gonadotrophin secretory pattern from birth to puberty between early and late maturing bulls. We also characterized the changes in semen morphology that occur about the time of puberty. Blood samples were collected (n=28) every wk from 2 to 20 wk of age and then every 2 wk until 50 wk of age. Semen was collected by electroejaculation at approximately 4-wk intervals from 36 to 49 wk of age. Puberty was defined as the first age at which an ejaculate contained 50 million spermatozoa with a minimum of 10 % motility Bulls were divided into early (n = 14) and late (n = 14) maturing groups based on the age at puberty (41.9 +/- 0.3 and 48.3 +/- 0.7 wk of age, respectively). There was a transient increase in serum concentrations of LH and FSH between 2 and 24 wk of age; LH concentrations were greater in early maturing bulls than in late maturing bulls at 12, 13, 15, 17 and 48 wk of age (P < 0.05). Serum concentrations of testosterone and FSH did not differ between groups (P > 0.05). As the bulls matured there was an increase in the percentage of normal and live sperm cells, cell motility and the number of cells per ejaculate (P < 0.05), and a decrease in the percentage of proximal droplets and knobbed acrosomes (P < 0.05). We concluded that, during the early rise in LH secretion, early maturing bulls had higher circulating LH concentrations than late maturing bulls. During the weeks preceding and following puberty there was an increase in the quality of semen collected by electroejaculation.

Journal Article↗
PubMed2005

Pregnenolone and dehydroepiandrosterone administration in neonatal rats alters the immunoreactivity of hippocampal synapsin I, neuropeptide Y and glial fibrillary acidic protein at post-puberty.

It is well documented that neurosteroids administered during the neonatal period influence the development of several brain systems. In our previous study, pregnenolone administered to rats during the neonatal period altered adenosinergic and dopaminergic functions in the striatum and cerebral cortex. The present study examined the effects of the treatment with pregnenolone and dehydroepiandrosterone (DHEA) from the postnatal day (P) 3-P7 on synapsin I (a marker for presynaptic terminals) and glial fibrillary acidic protein (GFAP: a marker for astroglia) levels in the hippocampus of Sprague-Dawley rats at 3 and 7 weeks of age. In addition, neuropeptide Y and dynorphin A immunoreactivity was measured. The administration of pregnenolone and DHEA to neonatal rats significantly altered the expression of synapsin I in the dentate gyrus and CA3 region at post-puberty but not at pre-puberty. A significantly greater expression of GFAP-immunoreactive astrocytes or processes was demonstrated in the pregnenolone- and DHEA-treated groups at both pre-puberty and post-puberty. A significant increase in the number and size of GFAP-immunoreactive astrocytes and in the extension of arborization was seen in the overall hippocampus. The number of neuropeptide Y-positive cells in the hilus region was also significantly increased in the neurosteroid-treated group at post-puberty. No differences were detected in dynorphin A immunoreactivity among the experimental groups. These results of this study suggest that pregnenolone and DHEA play an important role in the development of hippocampus.

Animals↗
PubMed2006

Effects of central infusion and immunoneutralization of growth hormone on the timing of puberty and plasma leptin levels in the female rat.

Growth hormone (GH) levels increase during puberty though its role in puberty onset is still unclear. An interaction is suggested between GH and leptin, as triggering factor of puberty. To evaluate the role of GH on the timing of puberty and its relation with leptin, we centrally administered recombinant human GH (rhGH; 1 microg/day) to normally fed or food-restricted (FR) prepubertal female rats, and monitored time of vaginal opening (VO). Median time of VO was equally postponed in FR animals and in normally fed rhGH-infused rats: median time of VO was respectively 35 and 34 vs. 27 d. Central infusion of rhGH in FR rats partially restored the delay in VO. Plasma leptin levels were increased in rhGH-infused animals, normally fed or FR. Centrally infused anti-rat GH (0.6 microg/day) did not affect plasma leptin levels, but advanced median time of VO (25 vs. 28 d) in pair-fed female rats but not in ad lib-fed animals. The effects of the centrally infused compounds appear to depend on the dietary regime imposed on the prepubertal animals. Furthermore, plasma leptin levels show no direct or predictive relation to the time of VO. The data indicate an involvement of GH in puberty onset, but do not explain the mechanism employed.

Animals↗
PubMed2006

Treatment with a subcutaneous GnRH agonist containing controlled release device reversibly prevents puberty in bitches.

In most species, continuous administration of GnRH agonists desensitizes the pituitary to GnRH, and blocks ovarian function. The aim of this study was to assess the effects of a novel controlled release device containing azagly-nafarelin (Gonazon) to prevent puberty in young Beagle bitches (mean age: 4.88 +/- 0.32 months). Gonazon containing 18.5 mg azagly-nafarelin (n = 10) or a placebo implant (n = 10) was administered subcutaneously. Throughout the 1-year treatment, estrus behaviour was monitored weekly. Plasma progesterone concentrations, as well as body weight and height, were measured monthly. Following implant removal, estrus detection and progesterone measurement were continued until occurrence of puberty in all bitches. Control bitches displayed puberty (estrus, followed by ovulation) at approximately 11.9 +/- 2.7 (range, 8-16) months of age. In contrast, none of the Gonazon treated bitches displayed puberty during the period when Gonazon was present. Following removal of Gonazon, resumption of estrus and ovulation naturally occurred (seven bitches) or was induced (three bitches) approximately 8.5 (1.2-14.3) months later. As a consequence, age of puberty of the Gonazon treated bitches was 25.5 +/- 5 (18-31) months. No clinically detectable side effects were noted in Gonazon treated bitches. Height at withers was unaffected by treatment. Changes in body weight with time were also unaffected by treatment. Implants were well tolerated and generally easy to remove. These data demonstrated that Gonazon safely, efficiently and reversibly prevents reproductive function for 1 year in prepubertal bitches.

Animals↗
PubMed2006

Oocyte pick-up in juvenile lambs affects neither onset of puberty nor their future fertility.

A study was designed to evaluate whether the time of onset of puberty and fertility of young ewe lambs would be affected by oocyte pick-up conducted in single or repeated sessions during the first months of lambs' live. Five groups of lambs from the Karagouniko breed were used (A-E each n=12). In group A no treatments were applied (control group) while, laparoscopical follicular aspiration (OPU) was performed early in the third, fourth and fifth month of lambs age (groups C-E, respectively). From the second to fifth month of their age, group B lambs were aspirated four times in monthly intervals. All lambs were weighed at birth, weaning, at second month and monthly thereafter until the eighth month of age. Progesterone priming and ovarian stimulation by serial FSH administrations proceeded each OPU session. To determine onset of puberty blood progesterone concentration was assayed in samples collected initially every week and after the seventh month of age twice weekly. From the seventh month a fertile ram was introduced in each group and oestrous behavior/mating was daily monitored and recorded. Pregnancy diagnosis was carried out by transabdominal ultrasound scanning 55 days after rams' removal. At the fourth and fifth month of age group B lambs were lighter (p<0.05) than controls, but this difference was later equalized. The time of onset of puberty did not differ between groups (p=0.069) and ranged between 224 and 270 days. Some animals (n=15) entered puberty with a full-length luteal phase having progesterone concentration greater than 1ng/ml, while others (n=32) exhibited one or two short luteal phases before luteal length restoration. During the first breeding season 41 animals were fertilized and maintained pregnancy to term, without noticeable differences between groups (p=0.555). During the second breeding season, all ewes were naturally served and lambed at the expected time. It is concluded that OPU in young dairy lambs does not affect the time of onset of puberty, the endocrine profile of the lambs and it does not compromise their future fertility even if it is applied at four successive months.

Age Factors↗
PubMed2005

Distinctive stress effects on learning during puberty.

Puberty is a time of significant change in preparation for adulthood. Here, we examined how stressful experience affects cognitive and related hormonal responses in male and female rats prior to, during and after puberty. Groups were exposed to an acute stressor of brief periodic tailshocks and tested 24 h later in an associative memory task of trace eyeblink conditioning. Exposure to the stressor did not alter conditioning in males or females prior to puberty but enhanced conditioning in both males and females during puberty. The enhancement occurred in pubescent females irrespective of the estrous cycle. In adulthood, sex differences in trace conditioning and the response to stress emerged: females outperformed males under unstressed conditions, but after stressor exposure, trace conditioning in females was impaired whereas that in males was enhanced. These differences were not related to changes in gross motor activity or other nonspecific measures of performance. The effects of acute stress on corticosterone, estradiol, progesterone, and testosterone were also measured. Stressor exposure increased the concentration of corticosterone in all age groups, although sex differences were only evident in adults. All reproductive hormones except estradiol increased with age in a predictable and sex dependent fashion and none were affected by stressor exposure. Estradiol decreased in male rats across age, and remained stable for female rats. Together, these data indicate that males and female respond similarly to learning opportunities and stressful experience before and during puberty; it is in adulthood that sex differences and the opposite responses to stress arise.

Aging↗
PubMed2003

Effect of dietary energy and protein density on body composition, attainment of puberty, and ovarian follicular dynamics in dairy heifers.

The objectives were to examine the effects of dietary energy and protein density on age and body composition at puberty, and on ovarian follicular dynamics during the pre- and peripubertal periods in Holstein heifers. In Phase 1, heifers were randomly allotted (n=10 per diet) at 100 kg body weight (BW) to diets with either low (P1L), medium (P1M) or high (P1H) energy and protein formulated for an average daily gain (ADG) of 0.5, 0.8 or 1.1 kg per day, respectively. During Phase 2 (P2), all heifers were fed ad libitum a common diet formulated for an ADG of 0.8 kg per day. Half the animals within the high (n=5) and low groups (n=5) entered P2 either at 12 months of age (P2H-12; P2L-12) or at 330 kg BW (P2H-330; P2L-330). Heifers fed P1H, P1M, P1L, and P2L-12 diets attained puberty at approximately 9, 11, 16, and 14 months of age, respectively (P<0.01). Urea space estimates of body fat and protein percent, and back-fat thickness, were lower in P1L heifers compared to P1H or P1M heifers at similar chronological ages (P<0.05) but did not differ at puberty (P>0.10). Compared to P1L heifers, P1H heifers had high amplitude LH pulses at 8 months, and high frequency low amplitude LH pulses at 10 months of age (P<0.05). The mean diameter (mm) of the dominant follicle was smaller (P<0.05) in P1L heifers (10.6) compared to P1H (12.8) or P1M (12.2) heifers at 8 months. Maximum size and growth rate of the nonovulatory dominant follicle increased with age (P<0.05) but did not differ between P1H and P1M heifers at puberty. The diameter (mm) of the nonovulatory dominant follicle, and the first and second ovulatory follicles were larger in P2L-12 heifers (14.0, 14.7, and 14.9) compared to P1M heifers (13.1, 12.5, and 11.9), while the peak progesterone levels and CL growth were lower (P<0.05) in the first cycle. In conclusion, dairy heifers attained puberty at a constant body weight and body composition independent of dietary manipulation, the size of dominant follicles increased with age in association with increased LH support, and heifers realimented from a low energy diet developed larger first ovulatory follicles and smaller CL with lower peak progesterone concentrations in the first cycle.

Animal Nutritional Physiological Phenomena↗
PubMed1997

Puberty and growth rate in thoroughbred fillies.

We measured progesterone and estradiol levels from birth to the beginning of adult life in 10 Thoroughbred fillies from the Equilia Stud Farm in Avaré SP, Brasil. The animals were measured and weighed monthly for the determination of body development and of a possible correlation between the rate of weight and height gain and the onset of detectable sex hormone levels. Jugular blood was collected twice a week and stored at -20 degrees C until assay of progesterone by a solid phase RIA with a sensitivity of 0.32 nmol L and of estradiol by liquid phase RIA adapted to low levels (3.67 pmol L ). The fillies were born with high serum levels of both hormones, which fell to undetectable levels by the first week of life. A variation in growth rate was observed, with the highest levels occurring from birth to the 3rd month of life, followed by a reduction until 15 mo of life, when fast growth was resumed. The monthly weight gain was 1.5% when the fillies reached puberty and 5.4% during the next month, (P < 0.05, Friedman test). During this second period of accelerated growth after the beginning of progesterone production at detectable levels (above 0.318 nmol L ), the parameters of skeletal growth did not differ (P > 0.05). The month of onset of puberty was the month of lowest weight gain in the life of the fillies, and it coincided with the highest insolation period. In conclusion, horses, like all other developed vertebrates, have a double pattern of development, with the acceleration observed at puberty depending on sex steroids, which in turn coincides with the highest insolation period. Gonadal activity characterized by serum progesterone levels was low from birth to the onset of puberty. After puberty the progesterone cycles were similar to those of adult animals with a mature hypothalamic-gonadal axis.

Journal Article↗
PubMed2002

Insulin resistance of puberty in African-American children: lack of a compensatory increase in insulin secretion.

Type 2 diabetes has been increasing in children, mostly affecting minority populations at around the age of puberty. Despite a multitude of studies demonstrating pubertal insulin resistance/hyperinsulinemia in white children, data are almost non-existent in African-American children. The aim of the present study was to investigate the impact of puberty on glucose metabolism, insulin sensitivity and secretion in African-American children. Twenty prepubertal and 16 pubertal African-American subjects participated. All underwent a 3-h hyperinsulinemic (40 mU/m(2)/min) euglycemic clamp to determine insulin-stimulated glucose disposal, and a 2-h hyperglycemic (12.5 mmol/L) clamp to assess first- and second-phase insulin secretion. Body composition was assessed by dual energy X-ray absorptiometry (DEXA) and visceral and subcutaneous abdominal adiposity with computed tomography (CT) scan at L4-L5. Total glucose disposal, glucose oxidation and non-oxidative glucose disposal were significantly lower in the pubertal group compared with the prepubertal one (53.8 +/- 3.9 vs. 72.2 +/- 5.0 micromol/kg/min, p = 0.009; 23.3 +/- 1.1 vs. 31.6 +/- 1.7 micromol/kg/min, p = 0.001; and 30.0 +/- 3.3 vs. 40.5 +/- 3.9 micromol/kg/min, p = 0.049, respectively). Insulin sensitivity was approximately 30% lower in the adolescents compared with the prepubertal children. However, first- and second-phase insulin secretions were not different between the two groups (971.4 +/- 180.6 vs. 1044.0 +/- 191.4 pmol/L and 999.6 +/- 159.6 vs. 955.8 +/- 142.2 pmol/L, respectively). In conclusion, despite approximately 30% lower insulin sensitivity in African-American adolescents compared with prepubertal children, insulin secretion is not higher. This is in contrast to published findings in white children in whom insulin secretion is higher during puberty. These racial differences in physiologic adaptation to puberty could play a role in the higher prevalence of type 2 diabetes in African-American children at the time of puberty.

Journal Article↗
PubMed1988

Timing of puberty by photoperiod.

Photoperiod cues play an important role in the timing of puberty in the female lamb. Removal and replacement of photoperiod cues by denervation of the pineal gland and timed melatonin infusions, respectively, indicate that the pathway for transmission of photoperiod information develops well before puberty. This is reinforced by manipulation of artificial photoperiods during various periods of development. Such approaches reveal that even in the first few weeks of life, the pattern of melatonin secretion accords with daylength and modulates prolactin secretion. Several months later, after internal, growth-related cues indicate that sufficient body size has been achieved to initiate reproduction, photoperiod history is used as an important predictor of reproductive success, and thus, whether puberty should occur. In the female spring-born lamb, the decrease in daylength in autumn is the critical cue for the initiation of estrous cycles. Experimentally, this may be achieved by surgically disrupting the pathway for transmission of photic cues after appropriate long-day exposure. In the autumn-born lamb and in the slowly growing lamb, sexual maturation may be masked by the transition into seasonal anestrus the following spring. In these young females, a decreasing photoperiod or "removal of long days" (surgical) is not necessary for puberty the following autumn. Sufficient photoperiod history may be acquired in such lambs that they enter puberty as a consequence of becoming refractory to the long days of summer. We hypothesize that the phenomenon of refractoriness reflects the expression of an innate rhythm of reproductive activity and that changes in daylength experienced early in life serve to synchronize this rhythm with the seasonal environment.

Animals↗