Age-related changes in secretion rate and post-secretory metabolism of growth hormone in swine.
The effect of age on growth hormone (GH) metabolism and GH-releasing factor (GRF)-induced GH concentrations were studied in 7 young (3 mo, 39 kg) and 7 old (30 mo, 156 kg) Yorkshire x Landrace female pigs. Jugular catheters were surgically inserted and 60 hr later total serum volume was determined. The following day, all animals were infused for 3 hr with GH (30.3 ng.min/kg B.W.) in order to calculate GH metabolic clearance rate (MCR), secretion rate (SR) and half-life (t 1/2). Two days later, 15 micrograms/kg of GRF was injected i.v. into all pigs. On a per animal basis, aging increased (P < .01) MCR (299 vs 132 ml/min), SR (714 vs 422 ng/min) and serum volume (6.6 vs 2.01), whereas t1/2 was unaltered (P > .1). Basal GH concentrations were lower in older pigs (P < .10) but the GRF-induced GH concentrations (measured as GH peak or area under the curve, AUC) were not affected by age (P > .1). Yet, when induced total GH secretion (AUC x MCR) and average total serum GH (mean GH post-injection x serum volume) were calculated per pig, these variables significantly increased between 3 and 30 mo of age. Basal IGF-I concentrations were lower in older pigs (P < .01), yet, there was a tendency (P = .10) for these pigs to show a greater IGF-I response to GH infusion. The present data therefore indicate that age alters both SR and post-secretory metabolism of GH.(ABSTRACT TRUNCATED AT 250 WORDS)
Farmer
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Agriculture Canada, Research Station, Lennoxville, Québec, Canada.
Lapierre
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Matte
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JJ
Brazeau
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P
D000375:Aging / Q000378:metabolism*; D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology; D006207:Half-Life; D007262:Infusions, Intravenous / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D008657:Metabolic Clearance Rate; D010902:Pituitary Gland / Q000378:metabolism; D013552:Swine / Q000378:metabolism*
D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone