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Biomedical subjects

D R Pieper

Publications and source records attributed to D R Pieper.

51 records · Page 3Linked to original sources
PubMed1984

Pituitary gonadotropin-releasing hormone (GnRH) receptor responses to GnRH in hypothalamus-lesioned rats: inhibition of responses by hyperprolactinemia and evidence that testosterone and estradiol modulate gonadotropin secretion at postreceptor sites.

Increased hypothalamic GnRH secretion appears to influence positively the number of pituitary GnRH receptors (GnRH-R). GnRH-R increase after castration in male rats, and this rise can be prevented by testosterone (T), anti-GnRH sera, or hypothalamic lesions. GnRH also increases serum LH and GnRH-R in hypothalamus-lesioned rats, and these animals injected with exogenous GnRH are, therefore, a good model in which to study the site of steroid feedback at the pituitary level. Adult male and female rats were gonadectomized, and radiofrequency lesions were placed in the hypothalamus. Males received T implants, and females received estradiol implants at the time of surgery. Empty capsules were placed in the control animals. Beginning 3-5 days later, animals in each group were injected every 8 h with vehicle (BSA) or GnRH (0.002-200 micrograms/day) for 2 days. After these GnRH injections, all rats received 6.6 micrograms GnRH, sc, 1 h before decapitation to determine acute LH and FSH responses. GnRH-R were determined by saturation analysis using 125I-D-Ala6-GnRH ethylamide as ligand. In males, GnRH injections increased GnRH-R. T inhibited acute LH and FSH responses to GnRH in all groups, but had little effect on GnRH-R, indicating that T inhibits gonadotropin secretion at a post-GnRH receptor site. In females, the GnRH-R response to GnRH was less marked, and only the 200 micrograms/day dose of GnRH increased GnRH-R, indicating that the positive feedback effects of estradiol at the pituitary level are also exerted at a site distal to the GnRH receptor. There was no positive correlation between the number of GnRH-R and GnRH-stimulated gonadotropin release in males or females. Female rats with hypothalamic lesions had markedly elevated serum PRL levels (greater than 300 ng/ml). Suppression of PRL secretion by bromocryptine resulted in augmented GnRH-R responses to GnRH, and GnRH-R concentrations rose to the same values induced in males. This suggests that hyperprolactinemia inhibits GnRH-R responses to GnRH in females by a direct action on the pituitary gonadotroph.

Animals↗
PubMed1984

The influence of blinding, olfactory bulbectomy, and pinealectomy on twenty four-hour plasma prolactin levels in normal and neonatally androgenized female rats.

The influence of blinding (BLD), olfactory bulbectomy (ANOS), and pinealectomy (PX) on 24-h plasma PRL levels was examined in normal and neonatally androgenized (NA) female rats. NA pups were treated at 3 days of age with 1.25 mg testosterone propionate. Surgery was performed on both NA and normal animals at 22-25 days of age. At 10 weeks of age, animals were vaginally smeared, and at 15 weeks, they were ovariectomized, injected with 0.5 mg polyestradiol phosphate, and fitted with atrial catheters for blood sampling. At 16 weeks of age, blood samples were taken over a 24-h period. In normal animals, BLD plus ANOS resulted in half of the animals exhibiting a diestrous vaginal smear, while the other half exhibited at least one vaginal estrus during the 7-day period when vaginal smears were obtained. Ovarian, oviductal, and uterine weights for blinded (BLD) plus olfactory bulbectomized (ANOS) animals exhibiting diestrous smears were significantly less than those of BLD plus ANOS animals exhibiting periodic vaginal estrus. Plasma PRL levels were lower in both animal groups compared with those in sham controls, but BLD plus ANOS animals with small ovaries had significantly lower plasma PRL and BLD plus ANOS animals with large ovaries. PX of BLD plus ANOS animals resulted in endocrine organ weights comparable to those in controls and elevated the plasma PRL levels to those observed in BLD plus ANOS animals with large ovaries. The PRL levels in BLD, ANOS, and pinealectomized animals, however, were still below those in sham control animals. Sensory deprived animals had peak PRL values at various times of day, and regrouping of the data from the peak PRL time for each animal suggested the presence of a free-running plasma PRL rhythm. In NA animals, a decrease was also observed in endocrine organ weights and plasma PRL for BLD plus ANOS animals similar to that observed for normal BLD plus ANOS animals. However, all animals in the NA BLD plus ANOS group responded with a constant diestrous smear, small ovaries, and low plasma PRL values. PX prevented the decrease in endocrine organ weights and plasma PRL observed in BLD plus ANOS animals. As in normal animals, NA animals also exhibited a free-running PRL rhythm when sensory deprived.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Effects of photoperiod, castration, and gonadotropin-releasing hormone (GnRH) on the number of GnRH receptors in male golden hamsters.

Maintenance of male golden hamsters on short photoperiod leads to testicular regression due to pineal gland-mediated inhibition of the hypothalamo-hypophyseal reproductive system. This study clarifies the dynamics of the action of GnRH at the pituitary level after short photoperiod-induced gonadal regression. In Exp 1, adult male golden hamsters were injected with BSA or varying doses of exogenous GnRH every 8 h for 3 days. There was no effect on the number of GnRH receptors, indicating that GnRH does not increase the number of its own receptors in hamsters as it does in rats. In Exp II, adult male golden hamsters were placed on a 14-h light, 10-h dark lighting schedule (LD 14:10) or LD 6:18. Nine weeks later, half of the animals on each photoperiod were castrated, and 10 weeks after initiation of the experiment, intact and castrated hamsters were decapitated. Intact hamsters on LD 6:18 had the expected reduction in serum LH levels and testicular weight compared to intact animals on LD 14:10. There was a postcastration rise in serum LH in both groups, but the increase was attenuated in the animals on short photoperiod. Castration of animals on LD 14:10 resulted in an increased number of GnRH receptors per pituitary, but this increase was at least partly due to an increase in pituitary weight. Intact animals on LD 6:18 had fewer pituitary GnRH receptors than intact hamsters on LD 14:10, but this decrease was not due solely to a decrease in pituitary weight. These results indicate that maintenance on short photoperiod results in a decreased number of pituitary GnRH receptors. In Exp III, intact animals on LD 6:18 responded to 1 microgram GnRH, sc, with an increment in LH secretion similar to that in intact animals on LD 14:10. Castration of animals on long photoperiod increased the LH response to GnRH, but castration of hamsters on short photoperiod did not. In conclusion, a reduced number of pituitary GnRH receptors may be involved in the testicular regression associated with short photoperiod in male golden hamsters.

Animals↗
PubMed1983

Influence of blinding, olfactory bulbectomy and pinealectomy on plasma prolactin levels in the neonatally androgenized female rat.

Female rats were neonatally androgenized (NA) by administering 1.25 mg of testosterone propionate at 3 days of age. At 21-23 days of age, groups of 12 animals each were blinded (BLD), olfactory bulbectomized (ANOS) and pinealectomized (PX) either alone or in combination. At 11 weeks of age all animals were ovariectomized, implanted with atrial catheters and given 0.5 mg polyestradiol phosphate. At 12 weeks of age, animals were attached to catheter extensions and blood samples obtained at 09.00, 11.00, 13.00, 15.00, 17.00, 19.00 and 21.00 h. The plasma prolactin (PRL) pattern of NA control animals consisted of elevated basal values at 11.00 and 13.00 h with an afternoon peak at 17.00 h. Anosmic and PX animals had a PRL pattern similar to that of the control. Animals BLD or BLD + ANOS had significantly lower plasma PRL values than sham-operated animals. Animals BLD + PX had PRL values comparable to PX alone. The diurnal PRL pattern observed for NA control animals was still evident in all experimental animals. Blinding + ANOS resulted in a significant decrease in ovarian and oviductal weights and attenuated the estrogen-induced increase in uterine weight. The evidence indicated that the elevated morning PRL levels observed in NA rats was not due to an altered function of the pineal gland and that BLD + ANOS blunted the action of exogenous estrogen on uterine weight.

Aging↗
PubMed1981

Pituitary gonadotropin-releasing hormone receptors. Effects of castration, steroid replacement, and the role of gonadotropin-releasing hormone in modulating receptors in the rat.

To study the role of gonadotropin-releasing hormone (GnRH) receptors in the regulation of gonadotropin secretion, we used D-125I-alanine6 des glycyl10 GnRH ethylamide (D-125I-Ala analog), a nondegradable, superagonist GnRH analog to assess GnRH receptors on rat pituitary membranes. Receptor affinity in intact adult rats was 5.0 X 10(9) M-1 and was unchanged after castration in both sexes. Castration of adult male and female rats produced a twofold increase in GnRH binding capacity by 7 d and binding capacity remained elevated for the subsequent 14 d. GnRH receptor number rose more rapidly after castration in males than females, and the time-course of receptor rise was similar to the increase in serum gonadotropin levels. The increase in GnRH binding capacity was prevented by gonadal steroid replacement at the time of castration in both sexes. Injections of the GnRH analog, D-Ser6 (TBu) des Gly10 GnRH ethylamide for 4 d produced a 70% increase in GnRH receptor number in intact male rats and testosterone-replaced castrates. The same regimen, however, failed to increase the elevated receptor numbers present after castration. Administration of rabbit anti-GnRH serum concomitant with castration inhibited the rise in both GnRH receptor number and luteinizing hormone. The changes in pituitary GnRH receptors parallel previously demonstrated changes in hypothalamic secretion of GnRH. Thus, GnRH probably regulates its own receptor in vivo and gonadal steroids may influence pituitary GnRH receptors by changing hypothalamic GnRH secretion.

Animals↗
PubMed1979

Influence of the pineal gland, olfactory bulbs and photoperiod on surges of plasma prolactin in the female rat.

The role of the pineal gland, olfactory bulbs and photoperiod in the regulation of the two daily surges of plasma prolactin in the pseudopregnant rat has been investigated. Pinealectomy had no effect on the surges of prolactin in pseudopregnant rats maintained on either a long (14 h light : 10 h darkness; 14L : 10D) or a short (2L : 22D) photoperiod, but olfactory bulbectomy decreased the nocturnal surge in animals maintained on 14L : 10D. This effect of bulbectomy was eliminated if the rats maintained on 14L : 10D were also pinealectomized. After cervical stimulation, bulbectomized rats maintained on a 2L : 22D photoperiod had nocturnal-type prolactin surges similar to those of intact rats maintained on the same photoperiod. These results indicate that the pineal gland andlength of photoperiod are not involved in the regulation of the surges of plasma prolactin in pseudopregnant rats but that the olfactory bulbs may enhance the nocturnal surge.

Animals↗
PubMed1977

Lack of a circannual cycle of daytime serum prolactin in man and monkey.

Serum samples were obtained from 7 subjects (6 men and 1 woman) in the morning (09.00 h) and in the afternoon (15.00 h) of each week for a period of 13 months and assayed for prolactin by RIA. In addition, 4 female monkeys were sampled once weekly in the afternoon for approximately two years. The data were analyzed for cyclicity by power spectrum analysis. In both species a serum prolactin circannual cycle was not obvious. In most subjects statistically significant (P less than 0.05) cycles were observed; however, there was considerable variability among individuals in the duration of the cycle, which ranged between 4 and 50 weeks. A similar result was also observed for the monkey data; here the cycles ranged between 7 and 51 weeks. The physiologic significance of these cycles is unknown at present. It is suggested that although there appears to be no diurnal serum prolactin circannual cycle, this does not rule out the possibility that there may be a nocturnal circannual cycle.

Adult↗