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Biomedical subjects

S D Michael

Publications and source records attributed to S D Michael.

At least 55 records · Page 3Linked to original sources
PubMed1980

Peripheral plasma concentrations of LH, FSH, prolactin and GH from birth to puberty in male and female mice.

Circulating concentrations of plasma LH, FSH, prolactin and GH in male and female mice were measured twice daily (12:00 and 24:00 h) by radioimmunoassay from birth to puberty. FSH concentrations in females were higher than in males from birth to about 16 days of age, then values in males rose while those in females fell. Prolactin levels in both sexes were low then increased slightly toward puberty with midnight levels being higher in the males and lower in the females. LH concentrations were relatively low in both sexes until Days 7-8 of age then showed distinct fluctuations. The fluctuations of GH in both sexes seemed to correspond to fluctuations in LH.

Animals↗
PubMed1980

Plasma gonadotrophins, prolactin and corticosterone concentrations in male mice exposed to high altitude.

Groups of sexually-naive male NFR/N mice were maintained at sea level or exposed to simulated altitudes of 18 000 ft (5486 m) or 22 000 ft (6705 m) for 1, 3, 7, 14 or 28 days. Plasma LH concentrations were slightly but not significantly depressed after 1 day of hypoxia. Plasma FSH values were reduced (P < 0.05) after 1, 7, 14 and 28 days of exposure to 22 000 ft when compared to the values in the other groups. Prolactin concentrations fluctuated considerably, but were not uniformly affected by high altitude exposure. Exposure to 18 000 ft resulted in an elevation of plasma corticosterone concentration (P < 0.05) for 3 days, which was followed by a decline to control group values, whereas at 22 000 ft corticosterone levels remained elevated. These findings indicate that plasma LH values are transiently reduced during the initial 24 h of exposure to high altitude and that plasma FSH concentrations are depressed in a sustained manner during severe hypoxia.

Altitude↗
PubMed1979

The role of the endocrine thymus in female reproduction.

Neonatal thymectomy in mice induces ovarian disturbances, indicating some relationship between the thymus and the ovaries. The mechanism of the relationship, however, is not fully understood. One approach to elucidating the complex relationship has been to measure circulating hormone levels in thymectomized animals and those with small thymus glands, and compare these levels with those found in control animals. The data indicate that a thymus-pituitary-ovarian axis exists and that thymus disturbances may hasten the aging processes of the ovaries.

Animals↗
PubMed1979

Plasma gonadotrophins and progesterone concentrations during various degrees of underfeeding in pregnant mice.

Daily reduction of the normal (ad libitum) food consumption by as little as 35% significantly reduced (P less than 0.05) the percentage of mice with implantation sites at Days 7 and 9 of gestation. Underfeeding decreased body weight and reduced the weight of the ovaries and uterus. Plasma progesterone was decreased (P less than 0.05) as dietary intake was restricted and was associated with regression of the corpora lutea. No significant alterations in the plasma values of LH and FSH were observed in mice underfed between Days 1 and 9 of pregnancy. The decrease in plasma progesterone in the absence of reduced LH values may indicate that progesterone secretion between Days 5 and 9 of gestation is not controlled solely by LH.

Animals↗
PubMed1978

Estrous cycle regulation in the whitefooted mouse (Peromyscus leucopus) with special reference to vaginal cast formation.

The estrous cycle of the whitefooted mouse (Peromyscus leucopus) was consistent with those described for most small rodents and closely resembled that of the house mouse and the rat in timing. The presence of the male did not accelerate puberty nor induce cycle synchrony, but was critical in establishing cycle regularity. Females isolated from influences of males never attained a pattern of concistent cycle length. Development of the vaginal epithelium during estrus was excessive in both isolated and non-isolated females, resulting in a "cast" of cornified epithelium which could be removed intact during metestrus. Casts removed during the making of vaginal smears measured up to 20 mm in length and still left a sufficient residue of cells which could be detected in all stages of the estrous cycle.

Animals↗
PubMed1978

Embryonic implantation, dietary intake, and plasma GH concentration in pregnant mice exposed to hypoxia.

Inseminated mice were: 1) exposed to 8% O2, 2) pair fed to mice exposed to 8% O2, 3) fasted at 21% O2 or 4) maintained at 21% O2 (control) between Days 1-3 of pregnancy. The frequency of embryonic implantation sites in mice was reduced by greater than 60% in 8% O2 exposed and pair fed animals, and by 100% in fasted mice. During the initial 24 h of exposure to 8% O2, a significant component of the body weight lost by hypoxic mice was associated with the reduction in dietary intake. The contragestational effects of hypoxia and fasting were attributed to the endocrine consequences of inanition induced by hypophagia and adypsia. Plasma samples collected at 6-h intervals revealed a significant reduction in GH concentration in treatment groups compared to the controls.

Animals↗
PubMed1977

Effects of experimentally-induced chronic hyperprolactinemia on testosterone and gonadotropin levels in male rats and mice.

We have examined testicular and pituitary function in inbred CD-F rats and DBA/2J mice with chronic hyperprolactinemia induced by grafting 4 anterior pituitaries from adult females of the same strain under the kidney capsule. Eight rats were given pituitary isografts and 9 were sham-operated; blood samples were collected at 4-7 week intervals, and the animals were killed 6 months later. One month after surgery, PRL levels in grafted rats were elevated (348 +/- 15 vs. 94 +/- 11 ng/ml; P less than 0.001), LH levels were depressed (16 +/- 3 vs. 59 +/- 9 ng/ml; P less than 0.001), but T levels were not affected (1.0 +/- 0.1 vs. 1.1 +/- 0.2 ng/ml). The elevated PRL levels in grafted animals did not decline during the subsequent 5 months, while LH levels increased slightly, and T levels remained indistinguishable from those in the controls. At the time of autopsy, FSH levels were reduced in grafted rats (230 +/- 40 vs. 501 +/- 108 ng/ml; P less than 0.05). Multiple pituitary isografts did not affect the weight of the testes or the ventral prostate, but increased the weight of the seminal vesicles (P less than 0.001). In 11 mice examined 5.5 months after receiving pituitary isografts, plasma PRL levels were dramatically elevated (330 +/- 35 vs. 27 +/- 2 ng/ml; P less than 0.001), but plasma T levels and testicular weight were not different from those observed in 12 sham-operated controls. The weight of the seminal vesicles in grafted mice was increased (P less than 0.01). In both rats and mice, chronic hyperprolactinemia did not affect plasma testosterone levels or testes weight and increased seminal vesicle weight.

Adrenal Glands↗
PubMed1977

Plasma testosterone during pregnancy in the mouse.

Levels of plasma testosterone (T) were studied throughout pregnancy and on the day of parturition in selected strains of mice. A dramatic midpregnancy increase in androgen occurred in both strains examined (peak on day 9). A second increase in plasma T was found during the latter half of gestation (days 14-17), at which time plasma estradiol levels were elevated.

Animals↗
PubMed1975

Surface defects in ventricular cells of brains of mouse embryos homozygous for the Loop-tail gene: scanning electron microscopic study.

Luminal surfaces in the mesencephalon and rhombencephalon in normal mouse embryos and those homozygous for Lopp-tail were studied by means of scanning electron microscopy. Ventricular cells in the ventrolateral regions of normal day-10 and -11 brains showed single apical cilia and microvilli, whereas those in ventromedial regions showed a dense network of microvilli and bulbous projections which tended to obscure the apical cilia and cellular outlines. Similar regional differences occurred in the Loop-tail brains, although there was a marked decrease in the number and density of microvilli and bulbous projections. At days 12-14 of gestation the latter brains also showed a flattening of cell surfaces, shallow depressions, and craterlike ruptures in the plasma membranes.

Animals↗