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Biomedical subjects

B E Piacsek

Publications and source records attributed to B E Piacsek.

At least 19 recordsLinked to original sources
PubMed1997

Chronic underfeeding increases the positive feedback efficacy of estrogen on gonadotropin secretion.

Reduced caloric intake has been shown to inhibit reproductive cycles in females of several mammalian species. Previous studies have shown that increased negative feedback efficacy of estrogen on gonadotropin secretion may be responsible. The present study was designed to test the alternate hypothesis that caloric restriction alters the positive feedback efficacy of estrogen on gonadotropin secretion. Adult, cycling female rats were placed on reduced food intake (R) equal to 50% of that consumed by ad/libitum-fed controls (C). When R rats stopped cycling, both R and C rats were ovariectomized (OVX) and immediately implanted subcutaneously with a Silastic capsule containing 100 microg 17beta-estradiol (E2). Blood samples were obtained at 0900-1000 hr and 1600-1730 hr on Days 2, 4, 6, 8, 10, 12, and 14 after OVX and implantation. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and E2 were measured by radioimmunoassay in duplicate aliquots. Results indicate that underfed female rats retain the ability to respond to elevated estrogen levels with an afternoon surge of gonadotropin which is present for at least 14 days for LH. By contrast, FSH surges in R rats became progressively smaller and were no longer significant after Day 10. The present results also demonstrate that the response of R rats to elevated estrogen levels is significantly greater than that of C rats on Days 2-4 for FSH and 2-14 for LH. It is concluded that an inability to respond to elevated estrogen levels with an afternoon LH surge is not the cause of the cessation of normal estrous cycles. The progressive decrease in the afternoon surge of FSH may be, at least partly, responsible for the decreased follicular development observed in underfed rats. Possible explanations of the enhanced LH response to the positive feedback of estrogen are discussed.

Animals↗
PubMed1991

Underfeeding alters the effect of low levels of estradiol on luteinizing hormone pulsatility in ovariectomized female rats.

Reduced food intake results in altered reproductive function in female mammals and previous studies have shown this to be due, at least in part, to an increase in the negative feedback efficacy of estrogen on pituitary luteinizing hormone (LH) secretion. This study attempted to elucidate the site (CNS vs. pituitary) of increased negative feedback efficacy of 17 beta-estradiol (E2) in underfed female rats. Rats (Holtzman) were fed either ad libitum (CR) or 50% of normal food intake (UR). All other conditions were identical for CR and UR. When UR stopped exhibiting vaginal cycles, they were ovariectomized (OVX) along with the CR exhibiting normal vaginal cycles, and implanted subcutaneously with Silastic capsules containing 0, 1.2, 2.4 or 4.8 micrograms E2. Six or 12 days after OVX, rats were cannulated in the left carotid artery under brief ether anesthesia. Starting 3 h after surgery, blood was collected sequentially through a peristaltic pump at 5-min collection intervals for 2 h. Sequential plasma samples were assayed for LH by RIA. Pulse analysis was performed using PC PULSAR. No significant differences in pulse frequency or amplitude were found between CR and UR either at day 6 or 12. However, the number of animals exhibiting detectable pulses was reduced in UR when compared to CR. At 12 days after OVX, 100% of CR showed detectable pulses at all doses of E2, while 100, 60, 50 and 17% of UR had detectable pulses at 0, 1.2, 2.4 and 4.8 micrograms doses of E2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Increased suppression of luteinizing hormone secretion by chronic and acute estradiol administration in underfed adult female rats.

These studies attempted to elucidate the relationship between estradiol and luteinizing hormone (LH) secretion in chronically underfed (R) adult female rats. Examination of the response to ovariectomy revealed a significant delay in the onset of the postcastration increase in LH secretion in R females compared to control (C) animals. Chronic estrogen treatment in the form of Silastic capsules containing varying doses of E2. The response of C females was dose-dependent, ranging from complete suppression at 10 micrograms E2/animal to an absence of inhibition at 2.4 micrograms E2/animal. The acute response of LH secretion to E2 administration in the ovariectomized female indicated an increased suppression of plasma LH at 6 and 24 h after a single s.c. injection of estradiol benzoate (EB) in R compared to C animals. There was no difference between R and C rats in the ratio of free to protein-bound estradiol in the serum. The results of these studies suggest that the negative feedback efficacy of estrogen on LH secretion is significantly enhanced by reduced food intake in adult female rats and may be responsible for the loss of reproductive cyclicity in these animals.

Animals↗
PubMed1988

Gonadotropin-releasing hormone sensitivity in underfed prepubertal female rats.

Studies were conducted to investigate the effect of reduced food intake on pituitary gonadotropin-releasing hormone (GnRH) sensitivity as a possible link in the delay of puberty by underfeeding. Immature female rats (30-32 days old at the start of each experiment) were used throughout the study. Rats on reduced food intake (R) received 60% of normal food intake beginning at the age of 21 days, whereas control (C) animals were fed ad libitum. In ovariectomized (OVX), estradiol benzoate-progesterone-treated R rats, low doses (less than 5 ng/100 g body wt) of GnRH injected intravenously produced higher serum luteinizing hormone (LH) concentration than in comparable C rats. No difference was found at 5 ng GnRH but response to high doses (15 and 45 ng/100 g body wt) was sharply reduced in R rats. No difference in serum follicle-stimulating hormone concentrations was found. In contrast to the OVX-steroid treated animals, in intact R rats, GnRH evoked higher serum LH concentrations at both low and high doses. These studies indicate that reduced caloric intake can affect pituitary GnRH sensitivity and that the effect depends on both the dose of GnRH and the internal, gonadal steroid hormone milieu.

Animals↗
PubMed1988

Testicular involvement in peripubertal gonadotropin levels and accessory sex organ weight of male hamsters.

This study evaluates the influence of testicular secretions during development in male hamsters on peripubertal gonadotropin levels. Castration or sham operations were performed on the day of birth (Day 1), Day 5, 10, or 20 of life. Repeated plasma samples on Days 20-60 at 10-day intervals were taken via orbital sinus puncture. Castrated animals received a subcutaneous testosterone capsule on Day 60 and were killed on Day 70. In addition, seminal vesicles and ventral prostate weights were taken in all animals at Day 70. Castrated animals, regardless of day of castration, had higher gonadotropin levels and suppressed sexual accessory organ weights. Animals castrated on the day of birth had lower luteinizing hormone (LH) levels than animals castrated on other days. Castration on Day 10 resulted in lower follicle stimulating hormone (FSH) levels. Males castrated on Day 20 were most sensitive to the negative feedback effect of testosterone on LH secretion, while Day 10 castrates had elevated FSH levels after testosterone exposure. Sexual accessory weights also differed depending upon the day of castration. Results point out the importance of testicular secretions on the developmental processes as well as the differing ages at which various systems may be influenced.

Animals↗
PubMed1985

Altered negative feedback response to ovariectomy and estrogen in prepubertal restricted-diet rats.

Studies were conducted to explore the hypothesis that the delayed sexual maturation of female rats induced by reduced food intake (R) may result partially from an altered negative feedback response to estrogen. Animals were placed on 60% of normal food intake at 20 days of age. Controls (C) were fed ad libitum. Rats were used for three different experiments at 31-32 days of age. In Experiment I, rats were ovariectomized (OVX) and injected subcutaneously for 4 days with varying doses of estradiol benzoate (EB). They were killed the day after the last injection. In Experiment II, rats were ovariectomized and killed in groups at 4, 12, 24, 48, 72, and 120 h after OVX. In Experiment III, they were castrated and 1 wk later received a single injection of 0.5 microgram EB. Groups were killed at 1, 2, 4, 8, and 24 h after injection. Sera from all experiments were assayed for follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Results of Experiment I indicate that the efficacy of EB for suppressing LH, but not FSH, secretion is increased significantly in R rats. In Experiment II, OVX resulted in a delayed increase in serum LH, but not FSH, concentrations of R rats when compared to C animals. Results of Experiment III indicate a delayed, but more prolonged, suppression of LH secretion by EB in R rats when compared to C rats. Prolactin secretion, on the other hand, increased earlier in R rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Neonatal androgenization in the male rat: evidence for central and peripheral defects.

Studies were conducted to evaluate the development of the reproductive axis of the male rat androgenized with low-dose, chronic exposure to testosterone. Male rats were implanted with a testosterone-containing Silastic capsule on the day of birth. Capsules were left in the animals for 10 days, 20 days or permanently. Results indicate that in androgenized (A) rats, the weights of the testes (T), ventral prostate (VP) and seminal vesicles (SV) were significantly depressed in most age groups when compared to controls (C), regardless of the duration of capsule retention. Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH) and prolactin (Prl) levels were not altered in adult (85 and 100 days old) A rats, but FSH and LH did show significant changes in young animals with testosterone-filled capsules. The efficacy of testosterone in promoting VP and SV growth, and increasing protein/DNA ratios in castrated A rats was significantly reduced compared to C rats, but it was increased with respect to suppression of LH secretion. Results suggest that a low, chronically administered dose of testosterone during the early neonatal period can produce permanent changes in the reproductive axis of the male rat and that these changes may be both central (hypothalamo-hypophysial) and peripheral (testes and accessory structures).

Animals↗
PubMed1978

Sexual maturation of male rats in continuous light.

Male rats were raised from birth in either continuous light (LL) or in 14 h light/10 h dark per day (LD) at 22 +/- 1 degree C. Food and water were administered ad libitum. Groups of rats were killed by decapitation at 14, 20, 25, 35, 41, 45, 51, 55, 58, 63, and 79 days of age. Testicular (TW), ventral prostate (VPW), and seminal vesicle (SVW) weights were measured. Serum concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), and androgens were quantified by radioimmunoassay. Results indicate no significant change in TW or spermatogenesis. Spermatozoa were first seen in the lumen of 10% of seminiferous tubules at 35 days of age in both LD and LL rats and by 42 days of age, 80% of tubules from both LD and LL rats contained spermatozoa in the lumen. A highly significant depression in accessory structure development (VPW, SVW) was observed as a result of LL exposure. Serum FSH levels in LL rats were depressed on days 45, 51, 55, and 58 but elevated at 79. Serum PRL concentrations were elevated in LL rats on days 41, 55, 58, 63, and 79, whereas serum androgen levels were depressed on days 58, 63, and 79. Results suggest that exposure to LL results in delayed maturation of the accessory structures in the reproductive system of the male rat possibly as a result of reduced FSH or elevated PRL levels, which in turn may modify the rate and pattern of LH and/or androgen secretion.

Animals↗
PubMed1978

Maturation of the pituitary-gonadal system in the male rat.

Serum FSH and testosterone concentrations reached maximum levels between 35 and 45 days of age, which coincided with the appearance of mature spermatozoa in the majority of seminiferous tubules. Spermatozoa were not observed in sections of the urethra until the age of 46 days. Serum LH concentrations were low (5-6 ng/ml) before Day 25, became highly variable (12-57 ng/ml) between Days 25 and 53 and remained consistently above 35 ng/ml thereafter. Serum prolactin levels rose significantly between 30 and 43 days of age. Maximum prolactin levels coincided with the start of accelerated growth in the prostate and seminal vesicle glands. Testicular weights relative to body weight reached a plateau by 35 days of age, while relative pituitary and adrenal weights decreased throughout the study period. It is suggested that spermatogenesis is not complete until FSH and testosterone reach maximum levels, while prolactin may be involved in the stimulation of accessory sex organ growth. The pronounced variation in serum LH concentrations during the maturation period may reflect a progressive change in the sensitivity of the hypothalamic-pituitary axis to the negative feedback of gonadal steroids.

Animals↗
PubMed1976

Vaginal opening and early estrous cycles in rats raised at a low ambient temperature.

Rats raised from day 2 of life at an ambient temperature of 10 degrees showed delayed vaginal opening when compared to controls raised at 22 degrees. Cold-raised animals were also lighter in weight at the time of vaginal opening and had significantly longer estrous cycles. Low temperature may cause these effects either by suppressing prolactin secretion or, more probably, by elevating thyroid hormone levels which in turn suppress serum gonadotropin concentrations.

Animals↗
PubMed1975

Effect of exposure to continuous light on estrogen-induced precocious sexual maturation in female rats.

Immature female rats, raised in either cyclic light (LD; 14 H LIGHT/10 H DARK) Or constant light (LL) were divided into 4 groups and given daily injections of estradiol benzoate (5, 10, or 25 ng) in 0.1 ml sesame oil starting at 24 days of age. Control animals received oil only. Injections were continued until vaginal opening (V.O.). Half of each group of animals was killed and dissected 1 day after V.O. Results indicate that both LL exposure and EB treatment accelerated sexual maturation (as indicated by the day of V.O.) with a significant interaction between the 2 treatments. Thre greatest difference in age at V.O. between LD and LL rats was observed at a dose of 10 ngEB/day. Body weights and uterine weights decreased with higher doses of EB, apparently reflecting the younger age at the time of V.O. No significant differences in ovarian weights were observed. Results are interpreted to indicate that increased exposure to light may change the sensitivity of the hypothalamic-pituitary axis to the positive feedback of estrogen.

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