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D M Baldwin

Publications and source records attributed to D M Baldwin.

At least 37 records · Page 2Linked to original sources
PubMed1984

Pituitary LH responsiveness to GnRH in vitro as related to GnRH receptor number.

The objective of this in vitro study was to determine whether the increase in the augmented phase of the biphasic luteinizing hormone (LH) response to gonadotrophin-releasing hormone (GnRH) and its enhancement by estradiol (E2) were associated with GnRH-stimulated increases in pituitary GnRH receptor concentration. Pituitary glands from 72 h ovariectomized (OVX), OVX + E2, or proestrous rats were perifused continuously with GnRH (12 ng/h). LH release was measured at 10-min intervals, and pituitary GnRH-binding capacity (GnRH-BC) was assessed at 0, 40, 80, 120, and 240 min after addition of GnRH. All treatment groups exhibited a biphasic pattern of LH release; initial (20-70 min) and augmented (120-240 min) mean rates of LH secretion (micrograms/h) were 1.78 and 3.92 (OVX), 6.40 and 16.67 (OVX + E2), and 2.79 and 18.64 (proestrus), respectively. Total LH release was significantly greater in the OVX + E2 and proestrous groups (44.0 and 45.8 micrograms) vs. the OVX group (12.4 micrograms). Throughout the GnRH infusion period, GnRH-BC did not change significantly in any of the treatment groups with the exception of the OVX group in which there was a transient small decrease at 80 min post-GnRH infusion. There were no significant differences between treatment groups in GnRH-BC at any time after infusion of GnRH. These results demonstrate that the acute and augmented phases of GnRH-stimulated LH release and the enhancement of this biphasic response by E2 occurs independent of any increase in GnRH-BC and suggest that these events are mediated by postreceptor mechanisms.

Animals↗
PubMed1983

An improved method for water vapor detection.

We describe improvements in and details for the construction, calibration and use of a device using a thermal conductivity cell for the measurement of low-level rates of water evaporation (E) from a small surface area. E is measured from 0.0 to 1.0 mg . min-1 with a correlation coefficient of 0.999 between measured and independently verified rates and amounts of water evaporation. Data are available as a recordable analog d.c. voltage as well as in digital display for E and for the amount of water evaporated during an operator defined time period. The device we describe is noninvasive and it is designed to be constructed of conventional components. It is useful not only for measuring transcutaneous water diffusion in normal and diseased skin, but also it is adequately sensitive and rapidly responding to follow thermoregulatory and psychogenic sweating in small (nom. 1.0 cm2) skin areas. It can also be used to measure accurately and precisely the rates at which water is adsorbed by and removed from inanimate materials, as well as to determine how much water they store.

Animals↗
PubMed1983

Characterization of the luteinizing hormone response to continuous infusions of gonadotropin releasing hormone using perifused pituitaries from intact, ovariectomized and steroid-treated rats.

Anterior pituitary glands obtained from rats at various stages of the estrous cycle and from short-term ovariectomized (OVX) rats with or without physiological replacement of estradiol-17 beta (E2) and/or progesterone (P), were perifused in vitro with continuous infusions (4 h) of gonadotropin releasing hormone (GnRH) (12 ng/h). In all treatment groups the in vitro pattern of luteinizing hormone (LH) release in response to GnRH was characterized by an initial low rate of LH release (initial phase; 20-70 min) followed by a significant augmented rate of secretion during the late phase (120-240 min) with the exception of the estrous and OVX + P groups in which LH was released at a constant rate. The total amount of LH released in response to GnRH was similar for glands removed on estrus, diestrus-I (D-I) and D-II, but increased significantly for glands removed on 0900 h proestrus with a further increase at 1400 h proestrus. Ovariectomy reduced the total LH released in vitro by 50-60% and 85-90% compared with estrous, D-I, D-II and proestrous groups, respectively. In vivo treatment of OVX rats with E2 restored the in vitro LH response to levels comparable to those in the 0900 h proestrous group while treatment with P + E2 further increased the rate of LH release in the initial phase to levels similar to those observed in the 1400 h proestrous group. In all treatment groups, addition of 5 microM cycloheximide to the perifusion media significantly inhibited GnRH-stimulated LH release during the late phase without significantly altering the initial LH response except in the OVX + E2P group in which it was partially inhibited. These results demonstrate that perifused pituitaries maintain their characteristic responsiveness to GnRH in vitro. Furthermore, they indicate that LH secretion in response to continual GnRH stimulation involves protein synthesis-independent and -dependent components. E2, in vivo, enhances the magnitude of both components in response to GnRH in vitro, while E2 + P may further enhance the initial in vitro response to GnRH through a protein synthesis-dependent mechanism.

Animals↗
PubMed1982

Pituitary responsiveness to LHRH stimulation in hamsters treated neonatally with monosodium glutamate.

Previous studies have shown that neonatal administration of monosodium glutamate (MSG) results in a clearly defined lesion of the arcuate nucleus which disrupts mechanisms regulating normal FSH but not LH secretion in the adult female hamster. The present study was designed to investigate the effects of neonatally administered MSG or hypertonic saline (control) on the in vivo and in vitro responses to LHRH in adult animals. In order to evaluate these responses under a comparable hormonal background, all animals were ovariectomized at 2-3 months of age and given 50 micrograms of estradiol benzoate 3 weeks later. 24 h later, animals were anesthetized with sodium pentobarbital and a blood sample taken for baseline levels of gonadotropins; they were immediately given 5 or 25 ng LHRH intravenously, and LH and FSH responses to LHRH were determined by sampling at 15-min intervals over a 1-hour period. Pituitary content of LH and FSH was determined in a similar group of control and MSG-treated animals which did not receive the hypothalamic hormone. Basal LH secretion, the dose-response of LH to LHRH, and the pituitary concentration or content were similar in control and MSG-treated hamsters. In contrast to LH, basal FSH levels were significantly lower, the FSH responses to LHRH were greatly attenuated, and a dose response to LHRH was absent in MSG-treated animals when compared to control values. Pituitary FSH concentration and content did not differ between control and MSG-treated animals. However, when pituitaries were removed, hemidissected, preincubated for 1 h, and incubated in the presence or absence of 8.5 x 10(-9) or 8.5 x 10(-10) M LHRH for 3 consecutive 1-hour periods, no differences were noted between control and experimental animals regarding basal (no LHRH) or LHRH-stimulated release of LH and FSH. These results suggest that the decreased basal FSH levels and the attenuated FSH response to LHRH observed in vivo in MSG-treated animals may be due to an alteration in a neural or extraneural component which is involved in regulating the release of FSH by LHRH and which is evident in the absence of a functional arcuate nucleus and/or develops directly as the result of the neonatal administration of MSG.

Animals↗
PubMed1976

Effects of limiting water intake on the rat estrous cycle with observations on LH, prolactin, and corticosterone.

By the fifth week of restricting water intake at 1100 to a 15-min period per day, estrous cycle lengths had shifted in most animals (31/40) from 4 to 5 days with the 5-day cycles usually consisting of 3 days of diestrus. In the 5-day cycling rats, plasma corticosterone peaked at 1100 and also at 1900 hr, the proestrous surge in plasma LH was not significantly changed, although the variation in individual animals was greater and the prolactin surge was prolonged. Similar prolonged cycles followed water restriction at 1800 hr with animals returning to regular 4-day cycles when given water to ad libitum. These results suggest that the alteration of the normal corticosteroid rhythm and/or changes in prolactin secretion may account, in part at least, for the changes noted in cycle length after restricting the water intake.

Animals↗