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Biomedical subjects

D C Johnson

Publications and source records attributed to D C Johnson.

At least 253 records · Page 14Linked to original sources
PubMed1976

Effect of thyroidectomy on rhythmic gonadotropin release.

Nonstress blood samples were obtained from intact and thyroidectomized (TE) male rats at 3-hr intervals over a 24-hr period via rapid decapitation. The animals were thyroidectomized when 40 days old and used 6 weeks later. Intact animals showed periodicity in serum LH (P less than 0.01) and prolactin (P less than 0.01). Both gonadotropins began increasing after 8 PM and peak levels occurred at 11 PM. In contrast, 24-hr periodicity was not observed in serum FSH. Corticosterone levels in these same serum samples showed the expected circadian periodicity. After TE, the 24-hr pattern in all gonadotropins was altered significantly. Serum LH increased (P less than 0.01) and circadian periodicity appeared to be absent. FSH and prolactin levels were increased and decreased, respectively (P less than 0.01), with serum prolactin showing a 9-hr phase shift. Prolactin began increasing at 2 AM and reached a peak at 8 AM. Corticosterone in TE animals showed a 24-hr rhythm similar to that of intact rats. These findings confirm our previous observations that nonstress serum LH and prolactin levels fluctuate with a 24-hr periodicity and suggest that the level of, and the phase angle betweeen, these rhythms is markedly influenced by pituitary-thyroid activity.

Animals↗
PubMed1975

An epizootic of bovine tuberculosis in Georgia.

A tuberculous beef animal was detected Aug 29, 1973, by a veterinary medical officer in a Georgia slaughter establishment. Animal identification and traceback eventually led to a purebred beef herd in Decatur County, Georgia. Investigation and tuberculin testing of 23,000 cattle in 350 herds revealed 11 Mycobacterium bovis-infected beef herds and resulted in the complete depopulation of 5 herds. The epizootic was confined to Georgia and was eradicated by April, 1975.

Animals↗
PubMed1975

Serum luteininzing hormone and follicle-stimulating hormone concentrations in immature femal rats treated with multiple injections and various amounts of luteinizing hormone releasing hormone.

Release of immunoreactive LH and FSH was induced in immature intact female rats by repeated injections of synthetic luteinizing hormone releasing hormone (LH-RH). Altering the dose of LH-RH (5, 10, 20, 50 ng) and the frequency of administration (every 10, 20, 30 or 60 min) over a period of 2 h produced a variety of serum LH and FSH concentrations and ratios. When the dose was a constant 20 ng but the frequency of injections was either 20 or 30 min, a steady state in serum gonadotrophin concentrations was reached within 1 h and the level remained the same during the second hour. When given every 10 min, 20 ng LH-RH produced a much higher concentration of both LH and FSH during the second hour of stimulation. Examination of the gonadotrophin levels after each injection of LH-RH showed that the pituitary response was variable in spite of a constant stimulus.

Animals↗
PubMed1975

Increased glycolysis in immature rat ovaries using endogenous gonadotropins secreted in response to exogenous luteinizing hormone-releasing hormone.

The rate of glycolysis, as indicated by in vitro lactic acid production, in ovaries from immature rats was stimulated by raising serum concentrations of endogenous LH and FSH by intravenous injections of luteinizing hormone-releasing hormone. The rate was shown to be a function of the serum concentration of gonadotropin but the response required the presence of elevated hormone levels for about 1 hr. These data are offered as further evidence for the lack of physiological importance of brief changes in pituitary function.

Animals↗