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Biomedical subjects

R K Christenson

Publications and source records attributed to R K Christenson.

At least 109 records · Page 6Linked to original sources
PubMed1983

Pubertal development of the boar: age-related changes in testicular morphology and in vitro production of testosterone and estradiol-17 beta.

The responsiveness of testicular tissue, in terms of testosterone (T) and estradiol-17 beta (E2) production, to human chorionic gonadotropin (hCG) stimulation in vitro was assessed during pubertal development of the boar. A morphometric investigation was conducted concurrently to quantitate Leydig cell and seminiferous tubule changes in the testes of developing boars. Testicular volume percentage of seminiferous tubules increased from 36% at 40 days of age to a maximum of 72% at 190 days of age. Increases in tubular diameter were from 65 micrometers at 40 days of age to 236 micrometers at 250 days of age. Testicular volume percentage of Leydig cells decreased from 40% at 40 days of age to 10% at 250 days of age. Leydig cell number increased rapidly to 130 days of age, remained constant through 160 days, and then increased steadily to 220 days of age. Volume per Leydig cell changed little from 40 to 130 days of age, increased by 75% at 160 days, and declined thereafter. Total Leydig cell weight increased steadily from 40 to 160 days of age and then declined slightly. The capacity of Leydig cells for T production and testicular tissue for E2 production was greatest (P less than 0.05) after hCG stimulation in boars that were 130 and 160 days of age. In addition, sensitivity, as judged by the regression coefficient of T or E2 production per Leydig cell on log dosage of hCG was greater (p less than 0.05) for T at 130 days of age and for E2 at 160 days of age. The data presented support the hypothesis that one factor in pubertal development of boars is an increased capacity and sensitivity of the testes to gonadotropin stimulation.

Aging↗
PubMed1983

Ovarian blood flow throughout the estrous cycle and early pregnancy in sows.

The association between ovarian arterial blood flow (OBF), as measured with electromagnetic blood-flow transducers, and the concentrations of progesterone, estrone and estradiol-17 beta in systemic blood were determined throughout the estrous cycle and the first 21 days of pregnancy in four sows (first day of estrus or mating=Day 0). Changes in OBF were positively correlated (P less than 0.01) with the concentrations of progesterone in systemic blood throughout the estrous cycle (requal+0.63) and early pregnancy (requal+0.65) and negatively correlated (P less than 0.01) with estrone (r=-0.53) and estradiol-17 beta (r=-0.51) during the estrous cycle, but not (P greater than 0.10) during early pregnancy. In nonpregnant sows, OBF was lowest at estrus, highest during the luteal phase, and declined precipitously after Day 14 in association with declining concentrations of progesterone and increasing concentrations of estrogens in systemic blood. Patterns of OBF and progesterone during the subsequent pregnancy of each sow were similar to those observed during the estrous cycle until Day 12. Between Days 12 and 15 of pregnancy, blood flow to the ovary and progesterone in systemic blood exhibited transient rises of 26% (P less than 0.01) and 20% (P less than 0.05), respectively. Both an ovarian vasodilatory and luteotropic effect of the conceptuses was demonstrated on days critical for maintenance of the corpora lutea during early pregnancy in this species.

Animals↗
PubMed1982

Uterine blood flow and uterine arterial, venous and luminal concentrations of oestrogens on days 11, 13 and 15 after oestrus in pregnant and non-pregnant sows.

Concentrations of oestradiol-17 beta and oestrone were measured in the uterine arterial and venous blood of anaesthetized sows on Days 11, 13 or 15 of the oestrous cycle or of pregnancy. Uterine arterial blood flow and the amounts of oestradiol-17 beta and oestrone in uterine flushings were determined in the same animals. In pregnant animals arterial and venous concentrations were significantly different (P less than 0.05) for oestradiol-17 beta on Days 11 and 13 and for oestrone on Day 15. Uterine content of both steroids was consistently greater in pregnant than in non-pregnant animals with a peak on Day 13. Uterine arterial blood increased from Day 11 to 13 of pregnancy then declined (P less than 0.08) by Day 15; no change in uterine blood flow occurred on the corresponding days of the oestrous cycle.

Animals↗
PubMed1982

The relationship of fetal weight to serum albumin and alpha-fetoprotein in swine.

The within-litter relationship of fetal weight to fetal serum albumin and alpha-fetoprotein (AFP) was investigated at d 30 to 40, 45 to 50, 50 to 60, 75 to 85 and 90 to 105 of gestation in swine. Regression equations were calculated on individual litters and regression coefficients pooled across litters within each gestational age group. Coefficients for the regression of albumin on fetal weight (microgram . ml-1 . g fetus-1) were significant over all groups and ranged from 22.5 +/- 6.6 to d 45 to 50 to .7 +/- .2 at d 95 to 105. There was no significant relationship between AFP levels and fetal weight at any gestational age. Unilateral ovariectomy-hysterectomy was performed before mating to study effects of uterine crowding on the relationship of fetal weight to AFP and albumin. Although the total number of ovulations was not different from controls, this treatment resulted in only about 1.3 more fetuses/uterine horn compared with controls at either d 40 or 60 of gestation. Fetal weights in crowded litters were not different from controls. However, AFP levels in fetuses from crowded litters were lower than in control fetuses at d 40 (4.5 +/- .1 vs 6.7 +/- .5 mg/ml). Albumin levels in crowded fetuses were significantly lower than in controls at d 60 (342 +/- 50 vs 653 +/- 41 micrograms/ml). Because none of these differences in albumin or AFP could be attributed to variation in fetal weight or fetal number at the time of sample collection, it is possible that more extreme uterine crowding earlier in development resulted in these differences. These results demonstrate that fetal serum albumin concentrations are related to fetal weight when analyzed on a within-litter basis and that unilateral ovariectomy-hysterectomy may affect serum concentrations of both AFP and albumin early in fetal development. Future studies involving the regulation of synthesis of these proteins at the cellular level during development should provide information as to how factors affecting overall fetal growth and development influence the expression of a single gene. Previously, such markers that are amenable to study early in development have been lacking.

Animals↗
PubMed1982

Pubertal development of the boar: testosterone, estradiol-17 beta, cortisol and LH concentrations before and after castration at various ages.

Forty-eight Landrace x Duroc boars were assigned at weaning to eight castration ages (40, 70, 100, 130, 160, 190, 220 and 250 d). Catheterization of the external jugular vein was performed 5 d before scheduled castration. Blood samples were collected every .5 h between 0800 and 1200 h, 2 d before (-2) and on d +1, +2, +3, +4, +8 and +16 after castration. Testosterone (T) was determined in serum samples collected every .5 h on d -2. Serum concentrations of estradiol-17 beta (E2), cortisol (C) and luteinizing hormone (LH) were quantified by radioimmunoassays in pooled (within boar) samples collected on d -2. In addition, LH was determined in pooled (within boar) samples collected on d +1, +2, +3, +4, +8 and +16 after castration. Mean concentrations of T and E2 (d -2) increased in a near linear (P less than .01) fashion with age of boar. However, T concentrations at 250 d of age had declined (P less than .01) to values similar to concentrations of boars at 130 d of age. Serum C concentrations (d -2) were lower (P less than .01) at 100, 130 and 160 d of age compared with an average C concentration of 19 ng/ml for all other age groups. Mean concentrations of LH (d -2) did not differ among any of the ages. Luteinizing hormone concentrations were elevated (P less than .01) within 1 to 2 d following castration at 40, 70, 100, 130 and 160 d of age. Serum T concentrations of individual boars varied greatly at all ages as determined by half-hourly sampling over a 4-h period. The results indicate that in the boar: (1) T concentrations increase as pubertal development progresses and decline as maturity nears; (2) E2 concentrations increase steadily through pubertal development; (3) C concentrations are depressed at 100, 130 and 160 d of age relative to concentrations before and after that period; (4) LH concentrations are constant during pubertal development, and (5) a decrease in the sensitivity of the negative feedback mechanism controlling LH occurs after 160 d of age.

Aging↗
PubMed1981

Effect of doubling daily energy intake during the last two weeks of pregnancy on pig birth weight, survival and weaning weight.

Eighty-eight multiparous sows of four breeds -British Landrace (BL), Chester White (CW), Large White (LW) and Yorkshire(Y)-were mated to boars of their own breed or another breed-BL, Hampshire (H) or Y-to form eight breed groups. All sows were fed daily 1,8 kg of a standard 14% protein gestation diet based on corn-soybean meal through day 100 of pregnancy (6,000 kcal digestible energy/day). From day 100 of gestation to parturition, each sow received either the basal diet (6,000 kcal digestible energy/day) or the basal diet plus 1.82 kg corn starch (12,000 kcal digestible energy/day). All sows were fed a 16% protein corn-soybean meal-based diet ad libitum from day 1 to day 28 of lactation. Energy intake during gestation had no effect on individual pig birth weight, percentage survival or 28-day body weight. There were differences among breeds in pig birth weight (P less than .01) and 28-day weight (P less than .01), and a breed X gestation energy level interaction (P less than .05) was found, but the biological significance is questionable because of the small sample size. Pigs that nursed before blood samples were taken had lower (P less than .01) hematocrit than pigs not allowed to nurse before blood sampling. Energy intake of the dam had no effect on the magnitude of the difference between nursed and nonnursed pigs. We conclude than the normal pregnant dam maintains blood glucose homeostasis during hyperalimentation, thereby rendering ineffective this approach to increasing neonatal growth and survival.

Animals↗
PubMed1981

Synchronization of ewes during anestrus: influence of time of year and interval to onset of estrus on conception rate.

The effects of progestogen-gonadotropin treatment on estrous response, ovulation rate and lambing response of crossbred ewes were examined at two times during the anestrous season (May-June and July-August). Each ewe group was treated with progestogen pessaries for 16 days and injected with 750 IU pregnant mare serum gonadotropin (PMSG) on days 17 and 32 to induce two consecutive estrous periods. Data accumulated from single-sire matings of 500 ewes indicated that estrous, ovulation and lambing responses did not differ (P less than .10) between ewes treated in May-June (92%, 2.5, 66%) and ewes treated in July-August (93%, 2.5, 67%). We concluded that there were no significant differences between reproductive responses of ewes synchronized during mid-anestrus (May-June) and those of ewes treated during late anestrus (July-August). For the May-June and July-August groups combined, estrous, ovulatory and lambing response were higher (P less than .05) during the first induced estrous period (76%, 3.0, 62%) than during the second (33%, 1.9, 43%). In both the first and second induced estrous periods, as interval from PMSG injection to onset of estrus increased, significant declines in ovulation rate, conception rate and ram marking activity were observed, particularly when onset of estrus occurred 72 hr or more after PMSG injection. These results indicate that the reduced lambing responses reported for ewes synchronized during anestrus may be due to increased asynchrony of reproductive events in the ewe, or decreased ram aggressiveness and fertility, or a combination thereof, as the interval from PMSG injection to the onset of estrus increases.

Animals↗
PubMed1981

Fertilization and embryonic survival in ewes synchronized with exogenous hormones during the anestrous and estrous seasons.

Causes of reproductive loss in ewes synchronized and mated during the anestrous season and during the normal breeding season were compared with those for natural cyclic ewes mated in season. Synchronization of ewes in season and out of season with progestogen: pregnant mare serum gonadotropin (PMSG) increased ovulation rate, but the percentage of ewes ovulating did not differ from that noted for untreated ewes mated in season. However, synchronized ewes exhibited markedly higher total reproductive losses, both in season (49%) and out of season (58%), than did untreated ewes mated in season (25%). The two primary sources of the increased reproductive loss in synchronized ewes were increased fertilization failure and increased embryonic mortality, regardless of season. The increased fertilization failure was accompanied by a decrease in the number of accessory sperm per ovum and decreased tubal sperm numbers. The increased embryonic mortality among treated ewes was associated with increased variation in stage of embryo development within ewe and advanced stage of embryo development, which indicated that asynchronies of timing of onset of estrus, ovulation and fertilization may have occurred in synchronized ewes. The high reproductive losses for ewes treated out of season was characterized by a marked increase in fertilization failure, compared with that observed for ewes treated in season, in addition to the relatively high embryonic mortality associated with the synchronization treatment. Semen quality of rams was lower out of season than in season. It was concluded that the reduced and more variable lambing response often obtained for ewes treated with progestogen: PMSG during anestrus may be due to decreased semen quality of rams and increased asynchrony of events in the ewe reproductive tract.

Animals↗
PubMed1980

Environmental influences on the postpartum animal.

Environmental influences on postpartum reproduction of the ewe, cow and sow are quite evident. Photoperiod predominantly controls the reproductive cycle of ewes lambing in the spring season and presents little problem in ewes lambing in the fall. The effect of hot ambient temperature and high humidity on ewes bred during anestrus and those bred after estrous cycles resume (late summer) needs study. In the southern regions of the United States hot ambient temperature and high humidity severely impair postpartum reproduction in cattle of European breeding. In the postpartum postweaned sow from southern states such as Minnesota, a marked reduction in reproduction during late summer and early fall has been reported. Presently, the physiological mechanisms by which hot ambient temperature and high humidity influence postpartum reproduction are not fully understood in the ewe and cow, and even less so in the sow. Hot temperatures and high humidity at the time of breeding of the ewe and cow reduce conception rates and subsequent pregnancy rates. Ewes and cows exposed to hot temperatures have increased rectal and uterine temperatures that may cause lower pregnancy rates. Altered hormonal levels and uterine blood flow have been associated with increased environmental, rectal and uterine temperatures.

Animals↗