Selection for growth rate or against back fat thickness in pigs is associated with changes in growth hormone axis plasma protein concentration and mRNA level

Selection for increased growth rate or decreased back fat thickness results in concomitant changes in endocrine and metabolic status. Growth hormone ( GH) changes in blood plasma concentration related to selection for growth r ate and fat deposition were reported in pigs. The molecular mechanisms regu lating selection-induced changes in GH plasma concentration remain largely unknown. We investigated selection-associated changes in GH axis parameters in 2 pig lines selected for increased growth rate (F-line), or decreased b ack fat thickness (L-line), respectively. First. we investigated selection- associated changes in GH pulse parameters, in both selection lines we found each generation a declining GH peak maximum concentration and area under t he GH curve. GH pulse width was not associated with generation number. In b oth lines generation number was associated with a declined pulse interval, indicating that the number of pulses per day increased on average with 1 pu lse per 24 h per generation. Second, plasma concentration of GH axis relate d Insulin-like growth factor-I (IGF-I) and insulin were investigated. Plasm a IGF-I concentration was not associated with generation number in the F-li ne. Mean plasma insulin concentration declined each generation in both line s. Third, we investigated changes in GH and Pit-1 mRNA levels. In both sele ction lines GH and Pit-1 mRNA levels increased approximately 50% each gener ation. The high SD of the GH mRNA levels in both lines may suggest that the GH mRNA levels are pulsatile in vivo. We postulate a molecular mechanism t hat may explain how selection is associated with increased GH mRNA levels a nd GH pulse numbers, while lowering GH release per pulse. (C) 2001 Elsevier Science Inc. All rights reserved.