Previous research from our laboratory demonstrated that n-methyl-d, l-aspartate (NMA), a potent
agonist of glutamate, increased growth hormone (GH) secretion in barrows and boars. To determine if
testosterone modulates NMA-induced GH secretion, Poland China
3 Yorkshire swine were challenged
with NMA in a model that compared GH responses in boars with those of barrows or barrows
treated with testosterone propionate (TP). Boars and barrows weighing 112.6
6 1.4 kg (mean
6 SE)
were fitted with indwelling jugular vein catheters. Barrows (n
5 16) were given i.m. injections of TP
(25 mg in corn oil) twice daily from d 0 to d 6. Boars (n
5 16) and control barrows (n
5 15) received
twice daily injections of corn oil. On d 6, blood was sampled every 15 min for 4 h. Two h after sampling
began, all animals received an i.v. injection of NMA at a dose of 2.5 mg/kg body weight. Mean
testosterone concentrations (ng/ml serum) were similar (P
. .1) for boars (8.1
6 0.8) and barrows receiving
TP (7.3
6 0.3), but were greater in both cases (P
, .05) than for barrows receiving corn oil
(.2
6 .01). Prior to NMA injections, mean GH concentrations were similar (P
. .1) among groups and
averaged 2.7
6 .2 ng/ml serum across treatments. Serum concentrations of GH after NMA increased
(P
, .05) similarly among groups and averaged 6.3
6 0.3 ng/ml across treatments during the 2-h
period after injection. These results were not supportive of a role for testosterone as a modulator of
NMA-induced GH secretion in male swine. © 2000 Elsevier Science Inc. All rights reserved.