Evidence for a Steady Rate of Secretion of Prolactin Following Suckling in the Rat

Abstract

The concentration of prolaetin in plasma of rats on day 14 of lactation increased rapidly to a maximum within the first 15 min of suckling following 8 h of nonsuckling and was maintained during the remaining 45 to 75 min of suckling. Fresh, hungry litters were substituted every 30 min to maintain teat stimulation. The pattern of change in prolactin concentration during suckling closely resembled one when rat prolactin was infused constantly for 60 min into the circulatiou of rats on day 14 of lactation and after 8 h of nonsuckling. By contrast a single rapid intravenous injection of rat prolactin to rats on day 14 and after 8 h of nonsuckling produced a temporal pattern of prolactin concentrations unlike that during suckling. We conclude that in rats at mid-lactation prolactin is not released during suckling in a large amount over a short time but rather is released in relatively small quantifies during each minute of suckling.