Leptin increases in vivo GH responses to GHRH and GH-releasing peptide-6 in food-deprived rats.
BACKGROUND
Leptin has recently been shown to have a stimulatory effect on basal GH secretion. However, the mechanisms by which leptin exert this effect are not yet clear. GHRH and GH-releasing peptide (GHRP)-6 are the two most potent GH secretagogues described to date.


OBJECTIVE
To determine if leptin could also enhance in vivo GH responses to a maximal dose of GHRH.


METHODS
Leptin (10microg i.c.v.) or vehicle was administered at random before GHRH (10microg/kg i,v.) or GHRP-6 (50microg/kg i.v.), to freely-moving rats with food available ad libitum and to (48h) food-deprived rats.


METHODS
Leptin and GH concentrations were measured by radioimmunoassay. Comparison between the different groups was assessed by the Mann-Whitney test.


RESULTS
In comparison with fed rats, food-deprived rats showed a marked decrease in GH responses to GHRH as assessed by the area under the curve (5492+/-190ng/ml in fed rats and 1940+/-128ng/ml in fasted rats; P<0.05) and GHRP-6 (3695+/-450 in fed rats and 1432+/-229 in fasted rats; P<0.05). In comparison with its effects in vehicle-treated rats, leptin administered to food-deprived rats markedly increased GH responses to both GHRH (6625+/-613ng/ml; P<0.05) and GHRP-6 (5862+/-441ng/ml; P<0.05).


CONCLUSIONS
These data suggest that the blunted GH response to GHRH and GHRP-6 in food-deprived rats is a functional and reversible state, and that the decreased leptin concentrations could be the primary defect responsible for the altered GH secretion in food-deprived rats.
Carro
E
E
Department of Physiology, Endocrine Area Complejo Hospitalario Universitario de Santiago, University of Santiago, Santiago de Compostela, Spain.
Seoane
L M
LM
Señaris
R
R
Casanueva
F F
FF
Dieguez
C
C
D000818:Animals; D005508:Food Deprivation / Q000502:physiology*; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D020738:Leptin / Q000494:pharmacology*; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D020738:Leptin; D009842:Oligopeptides; C041048:growth hormone releasing hexapeptide; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone