Effect of Prolactin on Neutrophils and Monocytes

Dr. S.P. Thorat, Department of Pharmacology Seth G.S. Medical College and K.E.M. Hospital, Parel, Bombay 400 012 (India) Prolactin is a polypeptide hormone of pituitary origin and induces pronounced physiological effects on growth, reproduction and osmoregu-lation in a number of species [1]. A variety of mammalian cells possess receptors for prolactin, including those of the mammary gland, liver, kidney, brain, prostate, testis and ovary [2]. Data is accumulating to suggest that prolactin may have a physiologic role in the regulation of humoral and cell-mediated immune responses. Specific prolactin receptors have been identified on human T and B lymphocytes [2-6]. However an exhaustive literature search revealed scant information [5] regarding the effects of prolactin on monocytes and neutrophils. The present study was conceived to explore whether prolactin had any effect on the phagocytic leucocytes of peripheral blood, i.e. neutrophils and monocytes. This study was approved by the Institution’s Ethics Committee. Twenty milliliter blood was collected into he-parinised tubes from the antecubital veins of 10 healthy, non-smoking, male volunteers after obtaining their written informed consent. The blood was layered on FicollHypaque (Sigma). Monocytes and neutrophils were isolated by the method of Boyum [7]. The monocyte count was adjusted to 6×105 cells per aliquot. Each aliquot was incubated for 90 min with a suspension of Candida al-bicans (1 × 106 organisms) and 0, 5,10 or 20 μg of prolactin (Sigma). Care was taken to keep the total volume of suspension constant while incubating with different prolactin concentrations. Monocyte phagocytosis and fungicidal capacity were assessed using the modified method of Lehrer and Cline [8, 9]. The phagocytic capacity of neutrophils was studied using Staphylococcus aureus by the method of Wilkinson [10], where 1 × 105 neutrophils were incubated with 1 × 106 S. aureus and 0, 5,10 or 20 μg of prolactin for 60 min. The results (expressed as mean ± SE) were analysed using Student’s t test. The phagocytosis of neutrophils in the control aliquot was 31 ± 0.93%. When exposed to 5 μg of prolactin, it remained 32.57 ± 1.43%. A statistically significant increase in phagocytosis was obtained at prolactin concentrations of 10 μg (36.7 ± 0.93%, Similarly, incubation with prolactin increased both percent phagocytosis and intracellular killing of C. albicans by monocytes in a dose-dependent fashion. The phagocytosis increased from 27.6 ± 0.45% in the control aliquot to 31.8 ± 0.63% at 5 μg (p < 0.001), 36.5 ± 1.06% at