title: Age-related changes in the secretion of growth hormone in vivo and in vitro in infantile and prepubertal Holstein bull calves.
abstract: The average concentration of GH in blood is high at birth and declines during the period of sexual maturation in bulls. The objectives of these studies were (1) to define age-related changes in vivo in the pulsatile secretion of GH from birth to puberty, (2) to determine whether pituitary cell content of GH and characteristics of the secretion of GH in vitro reflect age-related changes in vivo, and (3) to examine whether responsiveness to GH-releasing hormone (GHRH) and somatostatin (SRIF) in vitro changed with age in Holstein bull calves. In experiment 1, calves were bled every 15 min for 12 h at < 1, 12 and 42 weeks of age (n = 5/group), these being representative of infantile, juvenile and pubertal stages of development. Calves were killed 3 to 5 days later and the pars distalis of the anterior pituitary gland was enzymatically dispersed into a suspension of single cells. Aliquots of cells were extracted with 0.01 mol NaHCO3/l to determine the content of GH and cultured for 18 and 72 h. As expected, the average concentration of GH in plasma decreased with age (P < 0.001). The initial decrease in GH was caused by a reduction in the baseline concentration between birth and 12 weeks of age. There was a marked decrease in GH pulse amplitude between 12 and 42 weeks of age and a further reduction in the baseline concentration. In contrast, the pulse frequency of GH increased (P < 0.05) from < 1 week to 12-weeks of age and remained constant thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Dairy and Animal Science, Pennsylvania State University, University Park 16802.
authors.forename: J M
authors.initials: JM
authors.lastname: McAndrews
authors.forename: C M
authors.initials: CM
authors.lastname: Stroud
authors.forename: R D
authors.initials: RD
authors.lastname: MacDonald
authors.forename: W C
authors.initials: WC
authors.lastname: Hymer
authors.forename: D R
authors.initials: DR
authors.lastname: Deaver
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D002417:Cattle / Q000502:physiology*; D005434:Flow Cytometry; D013006:Growth Hormone / Q000097:blood / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D008297:Male; D009924:Organ Culture Techniques; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011863:Radioimmunoassay; D013004:Somatostatin / Q000494:pharmacology
chemical_list: D013004:Somatostatin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone