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Litters of 4-day postpartum lactating rats were removed for 8 hr and then replaced to permit suckling for 30 min. Suckling produced a significant increase in blood prolactin and GH levels. When L-dopa was injected into the mother rats just before suckling, the rise in blood prolactin was completely prevented but the increase in GH was greater than in the suckled rats not given L-dopa. When mother rats were injected with Somatostatin just prior to and 15 min after renewal of suckling, the blood GH elevation was completely abolished but the rise in prolactin was not prevented. These results suggested that catecholamines may be involved in the suckling-induced rise in blood prolactin and GH, and that Somatostatin may have a role in the suckled-induced increase in GH release.

SummaryWhen mature male rats were placed in a chamber at 40° for 30 or 60 min, there were significant decreases in serum TSH and plasma GH, and a five- to tenfold elevation of serum PRL. A temperature of 4° for 1 or 2 hr increased serum TSH, did not significantly alter plasma GH levels, and resulted in a significant fall in serum PRL. The observation that TSH and PRL responded oppositely to the same temperature changes suggests that different mechanisms regulate release of these two hormones under these conditions. The possible role of stress, and the interactions of the hypothalamic hypophysiotropic hormones and biogenic amines in the temperature-induced changes remain to be evaluated.Note in proof: Wettemann and Tucker (Proc. Soc. Exp. Biol. Med. 146, 908 (1974)) recently reported that cattle exposed to increased ambient temperature showed a significant rise in blood prolactin levels, whereas exposure to cold ambient temperature resulted in a significant fall in blood prolactin. Thus cattle and rats sho...

SummarySynthetic TRH (iv) can significantly increase serum prolactin in proestrous female and in normal and estrogen-primed male rats by 10 min after injection.