Abstract
Summary
A diurnal pattern of changes in plasma TSH concentrations was found throughout pregnancy in rats. TSH levels (~400 ng/ml) were highest at 0200 hr and 0600 hr and lowest (~240 ng/ml) at 1500 hr. The diurnal pattern in TSH levels changed between the first and second halves of gestation. Whereas TSH levels declined to basal levels by 0900 hr (X ~ 240 ng/ml) from Days 2 to 10, they remained high at 0900 hr (X ~ 400 ng/ml) from Days 13 to 22. The temporal correlation between the nocturnal secretion of TSH and PRL in the pregnant rat was discussed. Finally, a large increase in plasma TSH (X = 682 ng/ml) occurred 2-4 hr postpartum. This postpartum rise in hormone concentration appeared to result from pup-induced stimuli, i.e., suckling.
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