Absorption of orally administered bovine prolactin by neonatal rats

Neonatal rats received by esophageal administration 400 ng bovine prolactin (bPRL) in 0.5 ml of diluent. Blood serum was collected by decapitation at intervals of 15, 30, 45 and 90 min after administration. Pooled samples of rat sera were assayed for the presence of immuno-reactive bPRL using radioimmunoassay procedures validated for that purpose. Significant quantities of bPRL were detected in sera from 7- and 8-day-old rats at 30 and 45 min after oral administration. However, there was no bPRL detected in sera from 7-day-old rats at 15 or 90 min after administration. There was also an absence of detectable bPRL at 45 min after administration in rats between 9 and 14 days of age. Rats older than 8 days apparently lose the ability to absorb oral bPRL or become more able to degrade the hormone.