Disappearance Rate of Exogenous Prolactin from Serum of Female Rats

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Abstract
The disappearance rate of prolactin from the blood of female rats was assessed by bio-assay of the serum at intervals after intravenous injection. The intradermal pigeon crop sac method of assay was used. Dilution of the serum 1 to 3 and 1 to 15 with saline prior to assay obviated the inflammatory reaction between the skin and underlying crop sac of the pigeon and reduced the incidence of nonspecific responses which occurred with undiluted serum. The presence of bovine prolactin in dilute serum induced a moderate inflammatory reaction in some pigeons; ovine, porcine and murine (rat) prolactin in dilute serum did not. The serum concentration of each prolactin tested fell quickly within 1 min. after injection. The rate of disappearance slowed during the next 2-3 min., then followed an exponential course. The latter rate was used in estimating the biological half-life (t1/2/) of ovine (10-12 min.), murine (10 min.), bovine (3 min.), and porcine (3 min.) prolactin in the blood of adult castrate female rats. The t1/2 of ovine prolactin was considerably faster in lactating rats (3 min.) than in either castrate rats (10-12 min.) or intact rats with corpora lutea (t1/2 = 11 min.).