Prolactin in the cat: I. Pseudopregnancy, pregnancy and lactation.

Abstract

Prolactin (PrI) secretion patterns were investigated during pregnancy, parturition, lactation and the weaning period of 8 cats by means of a heterologous radioimmunoassay (RIA) using canine PrI antisera and canine reference standards (NIAMDD). Prl concnetrations began to increase during the sixth week of pregnancy (gestation period, 9.5 weeks) and were significantly higher from the seventh week through the last week of pregnancy (�-31.2 ± 5.1 ng/ml) compared to the first 5 weeks (X.7.0 ± 0.3 ng/ml). PrI values averaged 43.5 ± 4.5 ng/ml for the last 3 days of gestation. In the 5 animals that lactated for 6 weeks postpartum, PrI levels remained high (40.6 ± 7.2 ng/ml) for the first 4 weeks postpartum. Pri concentrations averaged 27.8 ± 3.1 ng/ml during the last 2 weeks of lactation, a significant decline from the previous 4 weeks (P<0.05). Following weaning, Prl concentrations decreased to approximately 15 ng/ml during the first week with basal levels obtained by the end of the second week. In the 3 nonlactating animals, basal levels of PrI were achieved by 1, 3, and 10 days postpartum. During pseudopregnancy (the period of luteal production of progesterone, nonpregnant state) there were no significant changes in Pr! concentrations observed with a blood sampling regimen of one daily morning sample (X-7.3 ± 0.6 ug/mI). From this study, the following conclusions were drawn: 1) It is possible to measure PrI levels in the cat with the canine Prl system. 2) Prl levels are elevated in the last one-third of pregnancy, presumably for the induction of mammary gland growth and lactogenesis. 3) With the suckling stimulus, PrI levels are elevated during the 6-week lactation period; however, during the last 2 weeks of lactation, PrI levels decline significantly to about one-half of the immediate postpartum levels. Following weaning, PrI concentrations return to basal levels within 1 to 2 weeks. 4) Coitusinduced pseudopregnancy (without lactation) has no significant effect on PrI levels.