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Biomedical subjects

A H Meier

Publications and source records attributed to A H Meier.

At least 73 records · Page 4Linked to original sources
PubMed1978

Extrapituitary regulation of the circadian rhythm of plasma corticosteroid concentration in rats.

Intravascular injections of adrenocorticotropic hormone in hypophysectomized rats were approximately 3 times more effective in stimulating increases in plasma corticosteroid concentration when given at the offset rather than the onset of the daily photoperiod (12 h:12 h light-dark cycle). Reversal of the photoperiodic schedule produced a reversal in the corticosteroid response after 5 days. Similar temporal variations in androgen and T4 responses to LH and TSH were not obtained. Although plasma corticosteroid concentrations were maintained at normal intermediate levels in rats with adrenal autotransplants, daily variations were not demonstrable. These results indicate that the circadian rhythm of plasma corticosteroid concentration is regulated by way of neural pathways to the adrenal.

Adrenal Cortex Hormones↗
PubMed1977

Daily rhythms of lipogenesis in fat and lean white-throated sparrows Zonotrichia albicollis.

Lipogenesis was assayed at 6 times a day in the migratory white-throated sparrow Zonotrichia albicollis by measuring the incorporation of label in liver and body lipid 4 h after injection of [3H] acetate. There were daily rhythms of 3H incorporation by liver lipid both in fat birds in the vernal migratory condition and in lean birds in the summer photorefractory condition. Most of the liver lipid incorporation of 3H was restricted to the late afternoon and early evening in both the fat and lean birds. In addition, the total liver incorporation was similar for both groups. On the other hand, nearly twice as much 3H was incorporated in the body lipid of fat birds as in that of lean birds, and a daily rhythm was present only in fat sparrows. Injections of prolactin given simultaneously with [3H] acetate early during the day (at a time when daily injections of the hormone can cause severe losses in body fat stores) drastically reduces liver and body lipid incorporation of 3H. However, injections of prolactin during the afternoon (when daily injections of the hormone produce large increases in body fat stores) have no apparent influence on the incorporation of label. Our results indicate that a principal difference between lean and fat birds resides in a greater capacity in fat birds to transport triglycerides from the liver, in which they are produced, to the body storage depots. The daily rhythm of prolactin in some temporal relations may cause fattening by increasing the transport capacity or cause loss in fat stores in other temporal relations by directly inhibiting hepatic lipogenesis.

Acetates↗
PubMed1976

Daily variations in the effects of disturbance on growth, fattening, and metamorphosis in the bullfrog (Rana catesbeiana) tadpole.

Bullfrog tadpoles subjected to the daily disturbance of water replacement demonstrated differences in the rates of growth and metamorphosis and in fatbody weights which depended on the time of day when water replacement occurred. Early daily disturbances stimulated larval growth whereas midday disturbances stimulated metamorphosis. The time when the daily disturbances caused fattening changed during metamorphosis so that younger tadpoles fattened when disturbed early in the photoperiod and older tadpoles fattened when disturbed at midday.

Adipose Tissue↗
PubMed1976

Daily variation in concentration of plasma corticosteroid in hypophysectomized rats.

A daily variation in the concentration of plasma corticosteroid hormone is present in hypophysectomized rats implanted with pellets of adrenocorticotropic hormone (ACTH) and thyroxine. Although ACTH is necessary to maintain a functional adrenal, and thyroxine is required to permit the expression of the plasma corticosteroid rhythm, a normal daily variation in plasma corticosteroid concentration does not appear to depend on the periodic release of pituitary hormones.

Adrenal Cortex Hormones↗
PubMed1975

Changes in the daily rhythm of plasma corticosterone concentration related to seasonal conditions in the white-throated sparrow, Zonotrichia albicollis.

Circadian variations in concentrations of plasma corticosterone were investigated in the white-throated sparrow maintained on short (10-hr) or long (16-hr) daily photoperiods. In addition, the plasma concentrations of corticosterone were determined throughout a day in birds that were in the reproductively photosensitive spring migratory condition, the reproductively photorefractory post nuptial molt condition, and the fall migratory condition. Distinct unimodal rhythms were found in photosensitive birds. The daily rise occurred 12 hr after the offset of light in birds kept on both the short and the long photoperiodic regimens. There was no discernible daily variation in photorefractory birds kept on a 16 hr daily photoperiod and there was a bimodal rhythm in the birds that were in the fall migratory condition. The results are consistent with an hypothesis that assigns an important role to the circadian rhythm of corticosteroid concentration in the photoperiodic mechanism controlling seasonal reproductive and migratory conditions in the white-throated sparrow.

Animals↗