Biomedical subjects

H D Johnson

Publications and source records attributed to H D Johnson.

At least 73 records · Page 4Linked to original sources

PubMed1975

Influence of environmental heat on peripheral plasma progesterone and cortisol during the bovine estrous cycle.

Plasm progesterone and cortisol were measured in jugular blood by competitive protein-binding assay. Six cycling, estrus-synchronized Guernsey heifers were followed for four consecutive estrous cycles under two controlled temperature (18.2 C, 55% relative humidity; and 33.5 C, 55% relative humidity) conditions. Prolonged exposure to heat of Guernsey heifers increased plasma progesterone on days 2 to 19 of the first cycle and only on days 2 to 8 of the second cycle. However, heat stress depressed plasma cortisol in both cycles and reduced the correlation coefficient between these steroids relative to specific stages of the estrous cycle.

Animals↗

PubMed1975

Infantile auditory exposure and unusual response to antipsychiotic drugs (38510).

Reserpine and prochlorperazine were administered in separate experiments to adult CAW:CF1 mice and to adult LVG:LAK hamsters that had recovered from audiosensitization induced by 30 sec of doorbell sound during a critical period of infantile development. In contrast to controls that showed tranquilization in response to these drugs, the previously audiosensitized animals o both species responded with a high incidence of convulsive seizures. The proconvulsant effect of reserpine and prochlorperazine in previously audiosensitized mice was present one hour after drug administration, but had subsided 20 hr post-administration. The proconvulsant effect of reserpine in previously audiosensitized mice was shown to be dose-dependent. The proconvulsant effect of reserpine in previously sensitized hamsters was present 100 days after reserpine and prochlorperazine are poorly understood, possible mechanisms are discussed. Environmental noise during early inantile development appears to have significant residual effects persisting into adult life. This study has shown that idiosyncratic responses to antipsychotic drugs in adult laboratory animals can result from infantile auditory exposure, and it is speculated that human idiosyncrasies to psychoactive drugs may be similarly based.

Animals↗

PubMed1975

Effect of heat and milk yield on bovine plasma glucocorticoid levels.

This study indicates that at 15 degrees higher producing cattle (milk yield) have higher plasma glucocorticoid concentrations compared to lower producing cattle with glucocorticoid levels appearing to be positively correlated with lactational intensity. Short term thermal (30 degrees) exposure for 18 hr resulted in glucocorticoid levels being markedly lower in high producing cattle compared to low producers. This shift at 30 degrees (after 18 hr) is possibly due to different time sequence of glucocorticoid response to thermal exposure between high and low producing cows. These data support the concept that glucocorticoids assist the animal in efficiently meeting the greater energy demand of lactation and further studies should be undertaken to denote free plasma levels and their utilization by dairy cattle at various levels of milk production.

Animals↗

PubMed1975

Effect of thyrotropin-releasing hormone (TRH) on bovine plasma thyroxine levels at 18.5 and 35 C.

Six mature nonlactating Holstein cows were subjected to a test procedure of a sham period (saline injection) of 10 days that prededed and followed each 14 day TRH treatment period at 18.5 and 35 degrees. The objective of this study was to determine the effect of intramuscular injection of TRH (400D 35 DEGREES. The results indicate that im administration of TRH is effective in elevating plasma thyroxine levels at both 18.5 and 35 degrees, but the response is diminished after 7 days at 18.5 degrees and ineffective in sustaining or elevating plasma thyroxine levels in cattle after 6 days of TRH administration at 35 degrees.

Animals↗

PubMed1975

Effect of thyrotropin-releasing hormone (TRH) on plasma glucocorticoids and thyroxine in cattle.

The repeated systemic infusion of TRH (200 mug, twice daily) was effective in repeatedly elevating plasma T4 levels (20-40 min postinfusion) for the 3 experimental days. The post-TRH treatment (saline infusion) exhibited a depression of plasma thyroxine levels, possibly explained by previous high thyroxine levels exerting a suppressive effect on the hypothalamic-pituitary-thyroid axis. A depression of plasma glucocorticoid levels was shown within 1 hr in both experiments after TRH administration. The results indicate that TRH administration (systemic) is effective in temporarily elevating thyroxine levels and simultaneously lowering plasma glucocorticoids in cattle.

Animals↗

PubMed1974