Age Associated Variations in Lymphocytic Growth Hormone Secretion in Cattle*

The lymphocytic growth hormone (GH) and nitric oxide (NO) levels were studied among three different age groups of cattle viz. cyclic adult cows (3-8 years of age), young female calves (2 weeks old) and growing female calves (6 months old). The effects of leptin, sodium nitroprusside (SNP) and N-nitro-L-arginine methyl ester (L-NAME) on the secretion of lymphocytic GH and NO were also studied. Lymphocytic GH in young calves (90.92±6.21 ng/12 million lymphocytes) and growing calves (86.15±9.94 ng/12 million lymphocytes) were significantly higher than in adult cows (59.42±3.92 ng/12 million lymphocytes) without any significant change in lymphocytic NO secretion with age. Incubation of lymphocytes with SNP could significantly increase lymphocytic GH secretion only in adult cows, while in 6 months old calves it significantly reduced the lymphocytic NO secretion. Thus suggesting that in young calves the secretion of lymphocytic GH is independent of leptin and NO dependent mechanism.