Release and Restoration of Pituitary Lactogen in Response to Nursing Stimuli in Lactating Rats.

Abstract

The effects of nursing stimuli upon release and subsequent restoration of lactogenic hormone from the hypophysis was studied in 2 strains of lactating rats on 14th day post-par turn. Wistar lactating rats produced litters which, when 14 days old, were almost as heavy as those of the much larger Sprague-Dawley mothers. There was 15% more pituitary gland/100 g in Wistar rats which, after 10 hours isolation of mother and litter, assayed 30% more lactogen than pituitaries of Sprague-Dawley mothers (3.50 and 2.44 units/100 g, respectively). The Reece-Turner pigeon intradermal method of assay was used. Following 30 minutes nursing there was a greater discharge of lactogen (33%) in Wistar (1.16 units/100 g) than in Sprague-Dawley rats (0.78 unit/100 g). About 1/2 prenursing level was restored in both strains within 2.5 hours postnursing but in one strain tested (Sprague-Dawley) restoration to prenursing level did not occur even 9.5 hours postnursing.