Up-regulation of lymphocytic growth hormone secretion during the luteal phase of cycle and early pregnancy

Abstract

Growth hormone (GH) has been shown to be produced and secreted by peripheral immune cells. Therefore, we studied the release of GH by lymphocytes, during various stages of pregnancy and estrous cycle in the cow. The effect of leptin on the lymphocytic GH release was also investigated. Estradiol-17β and progesterone concentrations in plasma were measured in all animals to confirm their reproductive status. Growth hormone levels measured in cell cultures during early pregnancy (days 60-80) and during the luteal phase were greater (p ≤ 0.01) than levels during follicular phase or mid (days 100-160) and late (days 240-245) pregnancy. Leptin treatment stimulated (p ≤ 0.05) lymphocytic GH release during mid-pregnancy when the basal GH levels were low. Changes in lymphocytic GH release and elevation of lymphocytic GH secretion by leptin during pregnancy and the absence of such effects in estrous cycle may indicate that leptin modulation of lymphocytic GH plays a role in the regulation of immune response during pregnancy.