Induction of growth hormone (GH) mRNA by pulsatile GH-releasing hormone in rats is pattern specific

• Published in: American journal of physiology: endocrinology and metabolism Vol. 278; no. 5; pp. E885 - E891
• Main Authors: Borski, Russell J, Tsai, Wellington, Demott-Friberg, Roberta, Barkan, Ariel L
• Format: Journal Article
• Language: English
• Published: United States 01.05.2000
• Subjects: Animals; Dose-Response Relationship, Drug; Female; Gene Expression - drug effects; Growth Hormone - blood; Growth Hormone - genetics; Growth Hormone - metabolism; Growth Hormone-Releasing Hormone - administration & dosage; Male; Periodicity; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Rats; Rats, Sprague-Dawley; RNA, Messenger - biosynthesis; Weight Gain - drug effects
• ISSN: 0193-1849; 1522-1555
• DOI: 10.1152/ajpendo.2000.278.5.e885

1  Department of Zoology, North Carolina State University, Raleigh, North Carolina 27695; and 2  Division of Endocrinology and Metabolism, Department of Internal Medicine, Department of Veterans Affairs Medical Center and the University of Michigan Medical Center, Ann Arbor, Michigan 48109 Growth hormone-releasing hormone (GHRH) is a main inducer of growth hormone (GH) pulses in most species studied to date. There is no information regarding the pattern of GHRH secretion as a regulator of GH gene expression. We investigated the roles of the parameters of exogenous GHRH administration (frequency, amplitude, and total amount) upon induction of pituitary GH mRNA, GH content, and somatic growth in the female rat. Continuous GHRH infusions were ineffective in altering GH mRNA levels, GH stores, or weight gain. Changing GHRH pulse amplitude between 4, 8, and 16 µg/kg at a constant frequency (Q3.0 h) was only moderately effective in augmenting GH mRNA levels, whereas the 8 µg/kg and 16 µg/kg dosages stimulated weight gain by as much as 60%. When given at a 1.5-h frequency, GHRH doubled the amount of GH mRNA, elevated pituitary GH stores, and stimulated body weight gain. In the rat model, pulsatile but not continuous GHRH administration is effective in inducing pituitary GH mRNA and GH content as well as somatic growth. These studies suggest that the greater growth rate, pituitary mRNA levels, and GH stores seen in male compared with female rats are likely mediated, in part, by the endogenous episodic GHRH secretory pattern present in males. pituitary; growth; pulsatility; sexual dimorphism