Abstract
Summary
1) The effects of nursing stimuli upon release and subsequent restoration of lactogenic hormone from the hypophysis has been studied in 2 strains of lactating rats on 14th day postpartum. 2) 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 one-half prenursing level was restored in both strains within 2 1/2 hours postnursing but in one strain tested (Sprague-Dawley) restoration to prenursing level did not occur even 9 1/2 hours postnursing. The influence of amounts of lactogen released in the two strains is discussed in relation to lactational performance.
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