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PubMed2005

[Effects on development of the testicle in diet-induced obesity rats].

OBJECTIVE: We established diet-induced obesity animal model and observed the influence of obesity on testicle of the male rats. METHODS: Rats in model group were fed with fat-enriched diet for 6 weeks. We measured the body weight and the testis weight and observed the development of testicle by microscope, and compared with those of control group. Meanwhile, we measured the serum levels of testosterone (T) and estradiol (E2). RESULTS: The average body weight in model group rats was higher 29% than that in control group at 6 weeks old, 30% at 9 weeks old. We observed under microscope that most of the convoluted seminiferous tubule developed no good in model group, the 4 layer cells was sparse and the arrangement of them was not in order. The testosterone to estradiol ratios(T/E2) in model group was significant lower then that of control group (P < 0.05). CONCLUSION: The fat-enriched fat diet can induce obesity. It influenced the development of the testicle. This probably related to decrease of the testosterone to estradiol ratios.

Animals↗
PubMed1993

The effects of feed restriction on reproductive function in Sprague-Dawley rats.

Although it is known that severe feed restriction (FR) and weight reduction (to 50-60% of control values) will sharply impair rat reproduction, few data exist on the effects of less severe body weight reduction. In the present studies, adult Sprague-Dawley rats were feed restricted and maintained at 90, 80, and 70% of control body weight (CBW) for up to 17 weeks. In females, this treatment had no effect on fertility or total number of implants per dam, but transiently increased the length of the estrous cycle and decreased by 20% the number of corpora lutea in the 70% CBW females. Ovary weight at necropsy was decreased only in the 70% CBW group. Liver and kidney weights varied with body weight. In males, fertility was not affected when they were mated to nonrestricted females. While prostate and seminal vesicles weight varied with body weight, testis and epididymis weights were unchanged by any degree of FR, as were the number of sperm in the cauda epididymis and the number of homogenization-resistant spermatids in the testis. The percentage motile sperm was slightly decreased at all levels of FR. These data show that the Sprague-Dawley rat is largely resistant to adverse reproductive changes caused by feed restriction to 70% CBW. These data should be of use in interpreting changes seen in toxicity studies that produce weight-reduce Sprague-Dawley rats.

Animals↗
PubMed1983

Limitations imposed by testicular blood flow on the function of Leydig cells in rats in vivo.

Testis blood flow per testis closely follows testis weight in rats made aspermatogenic by a single exposure of the testis to 43 degrees C for 30 min or 500 rad (5 Gy) of irradiation from a caesium source, or following ligation of the efferent ducts. Aspermatogenesis following these treatments was associated with only minor changes in the concentrations of testosterone in peripheral blood before stimulation with human chorionic gonadotrophin (hCG), and a reduced responsiveness to hCG when testis weight had fallen after heating. The concentrations of testosterone in testicular venous blood was normal or above normal during aspermatogenesis resulting from heat or irradiation, and only slightly reduced following efferent duct ligation. Consequently testosterone production (defined as the product of plasma flow and the veno-arterial concentration difference for testosterone) was markedly reduced during aspermatogenesis, both before and after stimulation with hCG. It appears that the reduced blood flow limits the amount of testosterone leaving the testis, and while the Leydig cells are capable under some circumstances of compensating partially for this fall by increasing the concentration of testosterone in the testicular venous blood, this compensation is not complete when there are severe reductions in blood flow. Therefore one can conclude that the mass of the tubules is the main determinant of testis blood flow and the Leydig cells must manage with what the tubules require.

Animals↗
PubMed2000

Cimetidine (Tagamet) is a reproductive toxicant in male rats affecting peritubular cells.

Cimetidine (Tagamet) is a potent histaminic H2-receptor antagonist, extensively prescribed for ulcers and now available without prescription. Cimetidine is a known testicular toxicant, but its mechanism of action remains uncertain. Rats were treated i.p. with cimetidine either at 50 mg/kg or 250 mg/kg body weight for 59 days. Accessory sex organ weights, but not testis weight, were significantly reduced in the high dose treated groups. FSH levels were significantly elevated in both treated groups, but testosterone levels were unchanged. A high degree of variability characterized testis histology, with most tubules appearing normal and some tubules (15-17%) partially lacking or devoid of germ cells. Morphometry showed that although seminiferous tubule volume was not significantly changed, the volume of peritubular tissue was reduced in the high dose group. There was extensive duplication of the basal lamina, lamina densa in both apparently normal spermatogenic tubules and severely damaged tubules. Apoptotic peritubular myoid cells were also found. TUNEL labeling confirmed extensive apoptotic cell death in peritubular cells, but revealed apoptosis of vascular smooth muscle. Given that 1) peritubular myoid cell apoptosis occurs in apparently normal tubules, that 2) basal lamina disorders are found, and that 3) peritubular cells are lost from the testis, it is suggested that the primary event in cimetidine-related damage is targeted to testicular smooth muscle cells. This is the first in vivo-administered toxicant to be described that targets myoid cells, resulting in abnormal spermatogenesis.

Animals↗
PubMed1987

Antispermatogenic effects of cyclophosphamide in the Syrian hamster.

Cyclophosphamide is an alkylating antineoplastic drug and has been shown to impair spermatogenesis after chronic exposures. The purpose of this investigation was to determine the effect of cyclophosphamide on sperm production in hamsters following subacute intraperitoneal (ip) exposures. The Syrian hamster, Mesocricetus auratus, aged 10-11 wk, received single daily ip doses for 4 d ranging from 10 to 250 mg cyclophosphamide/kg body weight. Control hamsters received an equivalent volume of phosphate-buffered saline solution. Testis weight, caudal sperm number, and sperm morphology were monitored for 12 wk. Cyclophosphamide failed to induce sperm abnormalities. Testis weight and sperm count were slightly suppressed at wk 1 and 4 before returning to normal at wk 12. This study showed that subacute doses of cyclophosphamide in hamsters did not significantly affect the sperm production as previously reported in other animals.

Animals↗
PubMed2006

Chronic ethanol perturbs testicular folate metabolism and dietary folate deficiency reduces sex hormone levels in the Yucatan micropig.

Although alcoholism causes changes in hepatic folate metabolism that are aggravated by folate deficiency, male reproductive effects have never been studied. We evaluated changes in folate metabolism in the male reproductive system following chronic ethanol consumption and folate deficiency. Twenty-four juvenile micropigs received folate-sufficient (FS) or folate-depleted (FD) diets or the same diets containing 40% of energy as ethanol (FSE or FDE) for 14 wk, and the differences between the groups were determined by ANOVA. Chronic ethanol consumption (FSE and FDE compared with FS and FD groups) reduced testis and epididymis weights, testis sperm concentrations, and total sperm counts and circulating FSH levels. Folate deficiency (FD and FDE compared with FS and FSE groups) reduced circulating testosterone, estradiol and LH levels, and also testicular 17,20-lyase and aromatase activities. There was histological evidence of testicular lesions and incomplete progression of spermatogenesis in all treated groups relative to the FS control, with the FDE group being the most affected. Chronic ethanol consumption increased testis folate concentrations and decreased testis methionine synthase activity, whereas folate deficiency reduced total testis folate levels and increased methionine synthase activity. In all pigs combined, testicular methionine synthase activity was negatively associated with circulating estradiol, LH and FSH, and 17,20-lyase activity after controlling for ethanol, folate deficiency, and their interaction. Thus, while chronic ethanol consumption primarily impairs spermatogenesis, folate deficiency reduces sex hormones, and the two treatments have opposite effects on testicular folate metabolism. Furthermore, methionine synthase may influence the hormonal regulation of spermatogenesis.

Animals↗
PubMed1991

Effect of an acute exposure of rat testes to gamma rays on germ cells and on Sertoli and Leydig cell functions.

Germ cells and Sertoli and Leydig cell functions were studied from 7 to 180 days after an acute exposure of 2-month-old rat testes to 9 Gy of gamma rays. Body weight, testis and epididymal weights were recorded. Sertoli cell parameters (androgen-binding protein, ABP, in caput epididymis and plasma follicle stimulating hormone, FSH) and Leydig cell parameters (plasma luteinizing hormone, LH, testosterone and prostate and seminal vesicle weights) were determined together with the number of germ cells and Sertoli cells. Irradiation did not affect body weight but significantly reduced testicular and epididymal weights from day 7 and day 15 post-irradiation respectively. The cells killed by irradiation were mainly spermatogonia and preleptotene spermatocytes engaged in replicating their DNA at the time of exposure, but all spermatocytes seemed damaged as they gave abnormal descendent cells. By day 34, only elongated spermatids remained in a few tubules and thereafter very little regeneration of the seminiferous epithelium occurred, except for one rat which showed a better regeneration. Levels of ABP decreased by day 15 when the germ cell depletion had reached the pachytene spermatocytes, whereas FSH and LH levels rose when the number of elongated spermatids decreased. Levels of testosterone and the weight of the seminal vesicles did not change; occasionally, the prostate weight was slightly reduced. These results support our hypothesis that pachytene spermatocytes and elongated spermatids are involved in influencing some aspects of Sertoli cell function in the adult rat.

Animals↗
PubMed2000

Changes in serum alpha2u-globulin levels in male rats given diethylstilbestrol and applicability to a screening test for endocrine-disrupting chemicals.

alpha2u-Globulin (AUG) is a major rat urinary protein, which has a molecular weight of 16 kDa (kidney type) or 19 kDa (native type). The biosynthesis of this protein is under multi-hormonal regulation. In this study, we investigated changes in serum AUG level and their association with changes in the reproductive organs of male rats after the administration of the estrogenic chemical, diethylstilbestrol (DES) at doses ranging from 0.01 mg/kg per day to 100 mg/kg per day by gavage for 14 days. Our aim was to establish basic data for the development of a new screening method for endocrine disrupting chemicals based on serum AUG levels. DES treatment decreased the weight of testes in a dose-dependent manner; and was accompanied by atrophic histopathological changes in testes. Testis weights were significantly decreased by the group given 1 mg/kg per day DES; however, histopathological abnormalities were found in the group given 0.1 mg/kg per day DES. In four of five animals in the group given 1 mg/kg per day there was no significant decrease in testis weight and only a slight or moderate degeneration of the pachytene spermatocytes. Despite these findings, serum AUG levels in this group decreased markedly, while the serum AUG level markedly decreased even in the animals with no histopathological change in the 1 mg/kg per day or 0.1 mg/kg per day groups with no histopathological change also showed decreased serum AUG level. These results suggest that the serum AUG level may be a sensitive parameter for detecting the activity of estrogenic chemicals in intact male rats. Although a uterotropic assay has been proposed for immature female or ovariectomized female rats and is currently undergoing validation studies internationally, there is no screening method for estrogenic chemicals in intact male animals. More data on AUG changes by treatment with other estrogenic chemicals are needed in order to determine the sensitivity and specificity of this response to estrogens. Nonetheless, an AUG-based screening test for estrogenic chemicals may be useful owing to its applicability to conventional toxicity studies and an apparently higher sensitivity of this parameter compared to organ weight change or histology of testis in intact male rats and applicability to conventional toxicity studies.

Alpha-Globulins↗
PubMed1995

Effects of short-term exposure to hydroxyflutamide in utero on the development of the reproductive tract in male mice.

To determine if and when short-term ablation of androgen action compromises the development of the male reproductive tract in mice, the androgen receptor antagonist hydroxyflutamide was administered orally to pregnant FVB/N mice and the reproductive tracts of the male offspring were examined when adult. Hydroxyflutamide (30 mg per day) for 5 days from day 11 to day 15 of gestation caused hypospadias in all male progeny. However, testis weights, seminal vesicle weights, and serum testosterone levels were not affected (p > 0.05) but caput-corpus epididymal weights were 15% lower than controls (p < 0.02). Shorter periods of treatment that included day 14 or 15 caused hypospadias, but treatments that did not include days 14 and 15 did not (p < 0.002). Hydroxyflutamide (30 mg, once or twice daily for 2 consecutive days) between days 15 and 20 of gestation demonstrated that androgen ablation on days 15 & 16 caused hypospadias, absence of prostate, and scrotal location of the seminal vesicles with abdominal testes (p < 0.05). Males exposed later in pregnancy had prostates, but the weights were reduced (p < 0.001); testes were scrotal and seminal vesicles were abdominal; caput-corpus epididymal weights were 15-30% lower than controls (p < 0.05), but the tubule contained large numbers of spermatozoa. Furthermore, testis weights, serum testosterone, and the response of the testis to a human chorionic gonadotropin (hCG) challenge in vitro were not compromised by hydroxyflutamide, and seminiferous tubules exhibited normal spermatogenesis. When males that had been exposed to hydroxyflutamide on days 13 & 14, 15 & 16, 17 & 18 and 19 & 20 were housed with sexually mature females, pregnancies resulted only from the day 19 & 20 treatment group. Thus, there are long-term effects caused by short-term blockade of androgen action at critical times during pregnancy and such effects could result in the inability to impregnate, irrespective of any externally visible indications of developmental anomalies.

Androgen Antagonists↗
PubMed2002

Effect of the AIN-93M purified diet and dietary restriction on survival in Sprague-Dawley rats: implications for chronic studies.

Survival, growth and dietary intake (DI) variables were monitored in a chronic 114-wk study in which male Sprague-Dawley rats [n = 120; National Center for Toxicological Research (NCTR) colony] consumed the AIN-93M purified diet ad libitum (AL), or an amount reduced by 31% of total AL intake inclusive of all macro- and micronutrients. The main objectives were to ascertain the survival characteristics of rats fed the AIN-93M diet and to determine whether dietary restriction (DR) increases longevity of rats fed this casein-based diet compared with the use of mixed-protein sources of the NIH-31 cereal-based diet in an earlier study. Body, liver, brain, the brain/body ratio, spleen, thymus and kidney weights, body length and body density were decreased (P < 0.05) by DR, whereas testis weight and skull length were not altered by DR. Significant age effects at 58 and 114 wk were found for body, brain, the brain/body ratio, liver and testis weights, and body density. Survival rates for the AL and 31% DR groups were 43.3 and 57.5%, respectively. Survival curves were not significantly different. The survival rate for AL rats fed the AIN-93M diet was not different from that of AL rats fed the NIH-31 diet (43.3 and 51.7%, respectively). However, the survival rate for 31% DR rats fed the AIN-93M diet was significantly lower than 25% DR rats fed the NIH-31 diet (57.5 and 87.5%, respectively) although both groups had similar body weights and energy intake at various ages. Nutritional components in the NIH-31 diet that are missing and/or reduced in the AIN-93M diet may interact with DR to increase 114-wk survival. Although the survivability, growth and anatomical results of this study suggest that the AIN-93M diet is suitable for chronic rodent studies, additional studies such as comprehensive histopathologic and physiologic investigations must be undertaken to complete the evaluation process.

Aging↗
PubMed1993

Secretion of transferrin in ovine seminiferous tubule cell cultures in response to FSH: influence of breed, season of birth and age of lambs.

The response of lamb Sertoli cells to follicle stimulating hormone (FSH) was investigated by measuring transferrin secretion in seminiferous tubule cell cultures throughout the non-pubertal and the prepubertal periods. Cells could be cultured from birth until they attained a testicular weight of 19 g. The characteristics of individual dose-response curves were compared according to the breed, season of birth and testicular weight of the lambs. At the same season of birth and within a given testis weight range, dose-response curves of Romanov and Ile-de-France lambs were similar. Within a given testis weight range, spring-born animals exhibited a higher maximal transferrin secretion than autumn-born lambs, but the ED50 was similar. The main factor of variation of the dose-response curve parameters was the testicular weight of the lambs: the amplitude of FSH response increased 3-fold from a testicular weight of 6 g onwards, i.e. from the appearance of spermatogonia in seminiferous tubules. The ED50 increased 5-fold from 11 g onwards, i.e. from the beginning of the prepubertal period. Thus, Sertoli cells become less sensitive to FSH as spermatogenesis develops in seminiferous tubules. This phenomenon is largely the result of higher phosphodiesterase activity and is greatly reduced by 1-methyl-3-isobutyl-xanthine (MIX).

1-Methyl-3-isobutylxanthine↗
PubMed1993

Effects of a single brief period of moderate heating of the testes on seminiferous tubules in hypophysectomized rams treated with pituitary extract.

An experiment was conducted to examine the appearance of the seminiferous tubule 20 days after a single exposure of the testes of rams to a scrotal temperature of about 42 degrees C for 45 min. Ten of the animals were surgically hypophysectomized and five were simultaneously heated; these rams were treated twice a day with ovine pituitary extract to avoid modifications in the negative feedback from the testes to the pituitary and consequent changes in gonadotrophin secretion. Six intact rams (three heated and three unheated) were also studied. The pituitary extract significantly increased the testis weight and spermatogonial multiplications from A1 spermatogonia onwards. Twenty days after the heat treatment, testis weight was significantly reduced by heating; both tubular and intertubular tissues were affected. The total length of seminiferous tubules per testis was not modified, whereas the mean seminiferous tubule diameter was significantly reduced after heating. The total number of Sertoli cells per testis was not significantly modified, while their mean cross-sectional nuclear area was significantly reduced by heat treatment. A decrease in the number of all germ cells except A0 spermatogonia, from A1 spermatogonia onwards, was observed. The number of round spermatids decreased by 95 and 90%, slightly more than the diplotene primary spermatocytes (76 and 77%) and elongated spermatids (79 and 85%) in hypophysectomized pituitary extract-treated and intact rams, respectively. Round and elongated spermatids would be derived from germ cells that were respectively leptotene and young pachytene primary spermatocytes at the time of heating, whereas diplotene primary spermatocytes would have been type B spermatogonia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2005

Genotoxicity and toxicological effects of acrylamide on reproductive system in male rats.

The toxicity of acrylamide was evaluated through mutagenicity of Salmonella, chromosome aberration of Chinese hamster lung fibroblasts, micronucleus formation in mice and reproductive toxicity in rats. Based on Ames test, acrylamide showed mutagenic potency for strains TA98 and TA100. Moreover, both chromosomal aberration assay and micronucleus assay indicated that acrylamide might have genotoxic potency; the chromosomal aberration frequencies were observed to be proportional to acrylamide concentrations of 5-50 mM, and acrylamide significantly increased micronuclei in peripheral blood cells of mice at doses of higher than 72.5 mg/kg. Male rats were treated with acrylamide at doses of 0, 5, 15, 30, 45, or 60 mg/kg/day for 5 consecutive days, and the toxicity of acrylamide was observed. In the group treated with the highest dose of acrylamide (60 mg/kg/day), the loss of body weight and reduced testis weight were observed. Also the epididymides weights were reduced significantly in all the groups treated with acrylamide. The number of sperms in cauda epididymidis decreased significantly in an acrylamide dose-dependent manner. Rats treated with 60 mg/kg/day of acrylamide showed several histopathological lesions in the seminiferous tubules. There were thickening and multiple layering of the tubular endothelium, and the formation of many multinucleated giant cells in seminiferous tubules. Taken together, acrylamide not only causes the genotoxicity of eukaryotic cells and mice but also shows the toxicological effects on reproductive system in male rats.

Acrylamide↗
PubMed1988

The rate of 2,5-hexanedione intoxication, not total dose, determines the extent of testicular injury and altered microtubule assembly in the rat.

Charles River CD rats (220 g) were intoxicated with 1.0, 0.5, or 0.25% 2,5-hexanedione (2,5-HD) in the drinking water for a total of 21, 35, or 69 days, respectively. All rats received a total dose of 131 +/- 2 mmol/kg 2,5-HD at dose rates ranging from 1.9 to 6.1 mmol/kg/day. Rats were sacrificed 4 weeks after ending intoxication to evaluate the extent of testicular injury. An exposure rate of 6.1 mmol 2,5-HD/kg/day produced uniformally low testis weights (49% of control) and severe germ cell depletion, while exposure at 1.9 mmol/kg/day gave normal testis weights and histology. Exposure at the intermediate dose rate of 3.8 mmol 2,5-HD/kg/day produced an intermediate degree of testicular injury. In a separate experiment, testis pyrrole content and microtubule assembly behavior were measured in rats exposed to 2,5-HD at the various dose rates for 3 weeks. The rate of intoxication determined the extent of biochemical abnormality. Rats exposed to 1.0, 0.5, or 0.25% 2,5-HD had microtubule nucleation times 55, 63, and 72% of control and pyrrole contents equivalent to 2.14, 1.40, and 1.18 nmol 2,5-dimethylpyrrole/mg testis protein. These data demonstrate that 2,5-HD-induced testicular injury, unlike the nervous system toxicity, is dependent upon the rate of intoxication independent of total dose.

Animals↗
PubMed1994

Investigation of numbers and motility of spermatozoa in reproductively active and socially suppressed males of two eusocial African mole-rats, the naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Cryptomys damarensis).

Reproductive tracts and spermatozoa from reproductively active and reproductively suppressed non-breeding males from two species of eusocial African mole-rats Cryptomys damarensis and Heterocephalus glaber were examined. In two captive colonies of Heterocephalus glaber, reproductive tracts from seven non-breeding males removed from their colonies, and housed singly for 5-6 weeks to cause reproductive activation, were compared with reproductive tracts from seven non-breeding males. The body weight of the separated, reproductively active males increased significantly (P < 0.01), and the mean testis weights relative to body weight of the reproductively active males were significantly larger (P < 0.05) than those of non-breeding males. The number of spermatozoa, in one half of the reproductive tract, was higher in active males than in non-breeding males (mean +/- SEM: 8.59 x 10(6) +/- 2.69 x 10(6) versus 1.78 x 10(6) +/- 1.43 x 10(6), respectively; P < 0.05). In addition, six of the seven reproductively active males, but only two of seven non-breeding males, had motile spermatozoa. A total of 28 wild Cryptomys damarensis from two colonies were examined in the field. The testis weights relative to body weight of breeding males (n = 7) were higher than those of non-breeding males (n = 19; P < 0.01), but the number of spermatozoa did not differ significantly between the two groups (0.13 x 10(6) +/- 0.06 x 10(6), n = 7 versus 0.29 x 10(6) +/- 0.14 x 10(6), n = 21, respectively). Breeding and non-breeding males produced similar numbers of motile spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Hormonal regulation of spermatogenesis in the hypophysectomized rat: FSH maintenance of cellular viability during pubertal spermatogenesis.

The potential for follicle-stimulating hormone (FSH) to promote germ-cell survival and the cellular sites of FSH action were studied using a gonadally maturing (pubertal), hypophysectomized (Hx) rat model in which residual testosterone (T) activity was blocked by injections of an androgen-receptor antagonist, flutamide. Recombinant human FSH was given to androgen-deprived and androgen-blocked male rats at 27 days of age to determine maintenance of individual germ-cell types at 35 days of age. Follicle-stimulating hormone significantly increased testis weights and tubular diameters as compared with Hx and Hx-flutamide controls, although testis weights in FSH-treated animals were significantly lower than in pituitary-intact animals. Morphometric assays to determine ratios of germ cells to Sertoli cells and to determine the number of germ cells present per hour of development showed that the population of type A spermatogonia in the early stages of the cycle was not responsive to FSH. Follicle-stimulating hormone had a marked ability to maintain cell viability in the rapid, successive divisions that begin in the latter part of the cycle and that continue through the next cycle (i.e., from type A1 to A4 and from intermediate spermatogonia to type B spermatogonia to preleptotene spermatocytes to leptotene/zygotene spermatocytes to young pachytene spermatocytes). The data also suggest T responsiveness of these cell types since the Hx-FSH-flutamide group showed lower cell viability at the aforementioned steps when compared with the Hx-FSH group. Too few cell types were present at subsequent phases of spermatogenesis to allow a sensitive determination of FSH activity in the maintenance of cell viability. The data show the potential of FSH in the absence or relative absence of T activity to maintain cell viability. These data support the concept of overlapping and synergistic (or additive) effects of T and FSH in the immature rat and identify the cellular sites of FSH action.

Androgen Antagonists↗
PubMed1991

Seasonal changes in the in-vivo activity of the luteinizing hormone-releasing hormone (LHRH) neural apparatus of male rabbits monitored with push-pull cannulae.

Intact sexually mature New Zealand White male rabbits, raised under natural lighting and temperature conditions, were isolated and housed in air-conditioned quarters, in a 12-h light:12-h dark cycle. Push-pull cannulae were implanted towards the tuberal region of the hypothalamus, and animals were perfused with modified Krebs'-Ringer phosphate medium for an average period of 4 h. Most rabbits were repetitively perfused over an average period of 3.7 months. Perfusions were grouped into seasonal periods of about 40 or 80 days through the entire 1-year cycle: (A) 23 November to 31 December (winter solstice period: N = 6), (B) 1 January to 23 March (winter: N = 10), (C) 24 March to 13 June (spring: N = 9), (D) 14 June to 23 July (summer solstice period: N = 23), (E) 24 July to 13 October (late summer-early fall: N = 7) and (F) 14 October to 22 November (fall: N = 4). Maximal and minimal values of mean release, mean amplitude and mean frequency from every animal in each block were obtained. In the summer solstice group (D), maximal mean (+/- s.e.) LHRH release levels were significantly greater (14.42 +/- 6.62 pg/10 min) than for all groups (A, 0.76 +/- 0.27; B, 1.59 +/- 0.39; C, 1.34 +/- 0.22; E, 1.33 +/- 0.33; and F, 1.18 +/- 0.11) while during the winter solstice period (A), minimal mean LHRH release levels (0.48 +/- 0.04 pg/10 min) were significantly lower than in all other groups (B, 1.43 +/- 0.41; C, 0.96 +/- 0.11; D, 7.25 +/- 4.12; E, 1.18 +/- 0.37; and F, 1.18 +/- 0.11). Maximal values were highest during the summer solstice period while the minimal values were lowest during the winter solstice period. The amplitude and frequency of the LHRH pulses showed changes similar to those observed with the mean LHRH release. For 1 year, an estimated left testis weight was measured in 4-7 rabbits every 2-5 weeks. The percentage estimated testis weight peaked in early August and reached minimal levels during the winter months. These data demonstrate that the rabbit LHRH neural apparatus is very sensitive to seasonal influences although animals remained in a fixed photoperiod during the entire duration of the experiment.

Animals↗