ONTOGENY OF PITUITARY GROWTH-HORMONE AND GROWTH-HORMONE MESSENGER-RNA IN THE CHICKEN

The changes in pituitary growth hormone (GH) mRNA levels have been determined by Northern blot analysis and laser densitometry during embryonic development and posthatch growth of white Leghorn cockerels. Pituitary GH mRNA levels were observed to progressively increase between 18 days of embryonic development to a maximum at 4 weeks of age (posthatch). Subsequently, pituitary GH mRNA levels declined between 4 and 8 weeks of age, and between 12 weeks of age and adulthood. Pituitary GH contents showed increases during embryonic development and posthatch growth that paralleled the rise in GH mRNA. The decline in pituitary GH mRNA levels between 4 weeks of age and adulthood occurs when GH secretion has been observed previously to decline.