The spinal nerves that constitute the lumbosacral plexus and their distribution in the chinchilla.

In this study, the spinal nerves that constitute the lumbosacral plexus (plexus lumbosacrales) (LSP) and its distribution in Chinchilla lanigera were investigated. Ten chinchillas (6 males and 4 females) were used in this research. The spinal nerves that constitute the LSP were dissected and the distribution of pelvic limb nerves originating from the plexus was examined. The iliohypogastric nerve arose from L1 and L2, giving rise to the cranial and caudal nerves, and the ilioinguinal nerve arose from L3. The other branch of L3 gave rise to the genitofemoral nerve and 1 branch from L4 gave rise to the lateral cutaneous femoral nerve. The trunk formed by the union of L4-5 divided into medial (femoral nerve) and lateral branches (obturator nerve). It was found that the LSP was formed by all the ventral branches of L4 at L6 and S1 at S3. At the caudal part of the plexus, a thick branch, the ischiadic plexus, was formed by contributions from L5-6 and S1. This root gave rise to the nerve branches which were disseminated to the posterior limb (cranial and caudal gluteal nerves, caudal cutaneous femoral nerve and ischiadic nerve). The ischiadic nerve divided into the caudal cutaneous surae, lateral cutaneous surae, common fibular and tibial nerve. The pudendal nerve arose from S1-2 and the other branch of S2 and S3 formed the rectal caudal nerve. The results showed that the origins and distribution of spinal nerves that constitute the LSP of chinchillas were similar to those of a few rodents and other mammals.

Administration of a nonpeptidyl growth hormone secretagogue, L-163, 255, changes somatostatin pattern, but has no effect on patterns of growth hormone-releasing factor in the hypophyseal-portal circulation of the conscious pig.

The activity of the growth hormone secretagog, L-163,255, on growth hormone (GH), growth hormone-releasing factor (GRF), and somatostatin (SRIF) levels was evaluated in a porcine model of hypophyseal portal blood (HPB) collection. Young, castrated pigs had HPB and jugular blood collected for approximately 300 min. The blood collection was divided into discrete periods: baseline (BL) approximately 180 min; GH response period (RSP) approximately 90 min; and positive control period following a GRF bolus, 30 min. RSP was divided into a dominant response period (DOM) and a tail (TL). The spontaneous relationship between HPB GRF and SRIF and peripheral GH during BL has been reported (Proc Soc Exp Biol Med 217:188-196, 1998). The apex of the GH pulse resulting from L-163,255 administration was nonrandomly associated (P < 0.05) with descending periods of SRIF troughs. Frequency and amplitude of GRF and SRIF pulses, and frequency and depth of SRIF troughs were not different between BL and the beginning of DOM (the 20-30 min of GH increase). GH AUC was significantly greater (P < 0.05) for DOM compared to BL and TL, and for TL compared to BL. GRF AUC tended to be greater (P < 0.1) for RSP compared to BL, but the majority of the increase was in the TL period. There were no significant differences in the SRIF AUCs between the sampling periods. Furthermore, in a separate experiment, fos activity (a marker of neuronal activation) in the hypothalamus of pigs was examined after either L-163,255 (1x or 4x), isotonic saline (control), or hypertonic saline (positive control) administration. There were no differences in fos activity in the GRF, SRIF, or CRH immunopositive neurons between L-163,255 treatment and control. The pituitaries of the L-163,255-treated pigs showed marked fos activation compared to the controls. In conclusion, L-163,255 in pigs has its primary effect at the level of the anterior pituitary.

Hypophyseal-portal concentrations of growth hormone-releasing factor and somatostatin in conscious pigs: relationship to production of spontaneous growth hormone pulses.

A method of collecting hypophyseal portal blood (HPB) in conscious pigs was used to show the relationship between GRF and somatostatin (SRIF) concentration and peripheral GH response. Six male castrate pigs (approximately 63 kg body weight) had HPB and jugular blood collected individually for an average of 175 min each. Twenty-seven spontaneous GH pulses were detected in the 1050 min of total HPB collection. Of the associations examined, the only significant finding was that GH pulse maxima occurred nonrandomly within periods of SRIF descent (63%; P = 0.005). Although 48% (13/27) of GH pulse maxima were associated with an ascent in portal GRF concentration, these associations were not determined to be nonrandom (P = 0.14). Only 7 of 27 (26%) GH pulse maxima were associated with an ascent in portal GRF concentration and a descent in SRIF concentration occurring simultaneously. A saline infusion given approximately 120 min after beginning blood collection resulted in an increase in SRIF pulse frequency and a decrease in GH-AUC and GRF-AUC. The cause of this saline effect is unknown, but it may have been related to acclimation of the pigs to the blood collection procedure. These data show the complexity of the relationship between SRIF and GRF concentrations and GH secretion and may indicate a close relationship with SRIF in GH pulse generation in the pig. In addition, these data support the hypothesis that, in the pig, mediation of GH release cannot be explained simply by antagonism between GRF and SRIF.

Growth hormone (GH) and insulin-like growth factor I responses after treatments with an orally active GH secretagogue L-163,255 in swine.

L-163,255 is a potent orally active spiropiperidine GH secretagogue. When administered iv or orally, L-163,255 caused GH to be increased in a dose-related manner, with a return to baseline by 90 min. After iv administrations of saline and L-163,255 at 1, 3, and 10 micrograms/kg, GH areas under the curves (GH AUCs) over 120 min were 377 +/- 136, 1151 +/- 413 (P < 0.05), 795 +/- 413 (P = NS), and 1770 +/- 416 ng.min/ml (P < 0.01), and peak GH concentrations were 8 +/- 3, 16 +/- 7 (P = NS), 17 +/- 5 (P = NS), and 43 +/- 12 ng/ml (P < 0.01), respectively. No changes in plasma cortisol concentrations were noted. After oral administrations at 3, 10, and 30 micrograms/kg, GH AUCs over 180 min were 1133 +/- 154, 1246 +/- 129 (P = NS), and 1551 +/- 210 ng.min/ml (P = NS), and peak GH concentrations were 7 +/- 2, 11 +/- 3 (P = NS), and 23 +/- 6 ng/ml (P < 0.01), respectively. After administration in feed, L-163,255 caused a dose-related increase in GH, with an initial peak observed at 60 min for both 30 and 300 micrograms/kg dose groups, and remained elevated above baseline through 180 min for the high dose group only. GH AUCS for 180 min posttreatment were 929 +/- 134 and 1897 +/- 244 ng.min/ml, and peak GH concentrations were 9 +/- 2 and 22 +/- 4 ng/ml for the 30 and 300 micrograms/kg doses prepared in 150 g feed, respectively. When provided in feed ad libitum over the 72-h period, mean plasma insulin-like growth factor I levels increased 15%, 62% (P < 0.01), and 109% (P < 0.01) in the untreated, treated with L-163,255 at 360 ppm, or treated with porcine somatotropin groups, respectively. Repeated iv administration of L-163,255 at 1 mg/kg once daily over 14 days resulted in an initial marked GH response, followed by a much reduced, but significantly elevated, GH response over the saline control values on subsequent treatment days. Repeated iv treatments with L-163,255 also resulted in an elevated insulin-like growth factor I level (approximately 60%) over that in saline controls. Compared to those in saline controls, plasma cortisol concentrations tended to be increased after the initial dose of L-163,255, but no significant increases were noted on days 7 and 14 in the L-163,255 group. The results of these studies indicate that L-163,255 is an orally active GH secretagogue suitable for long term efficacy studies in swine.

Mediation by the central nervous system is critical to the in vivo activity of the GH secretagogue L-692,585.

To investigate the effect of hypophyseal transection (HST) on GH secretagogue activity of the non-peptidyl GH secretagogue L-692,585 in the conscious pig, male castrated swine were randomly assigned to either a hypophyseal stalk transection group (HST; n = 3) or to a sham-operated control group (SOC; n = 3). Treatments administered were L-692,585 (100 micrograms/kg), human GH-releasing factor(1-29)NH2 (GRF; 20 micrograms/kg) or L-692,585 (100 micrograms/kg) + GRF (20 micrograms/kg) on days -7 to -3 before surgery and days +3 to +8 after surgery. To evaluate the integrity of the pituitary gland, the animals were challenged with corticotropin-releasing hormone (CRH; 150 micrograms) or GnRH (150 ng/kg) both before and after surgery. Blood was collected from -60 to +180 min post treatment and assayed for GH, cortisol and LH. Before surgery, no significant difference (P > 0.05) in peak GH response (ng/ml) was present between the two groups (SOC vs HST) in response to L-692,585 (101 +/- 12 vs 71 +/- 9) or L-692,585 + GRF (171 +/- 21 vs 174 +/- 21). Only two out of three SOC vs three out of three HST pigs responded to GRF (13 +/- 2 vs 25 +/- 3) resulting in a significant difference between groups. Following surgery, significant differences were present in peak GH response (ng/ml) between SOC and HST groups following L-692,585 (79 +/- 6 vs 13.8 +/- 1.0); however, the response to L-692,585 + GRF was similar (115 +/- 8 vs 94 +/- 7). All animals responded to GRF; however, a significant difference was present between groups due to the magnitude of the responses. Whereas the cortisol responses (ng/ml) to L-692,585 in the SOC and HST groups were similar before surgery, a significant difference was present after surgery (44.4 +/- 6.4 vs 14.6 +/- 2.1). No significant difference was noted between the HST and SOC groups in response to CRH or GnRH either before or after surgery. These results indicated that L-692,585 induced an immediate GH response in the intact animal in contrast to GRF where the GH release was variable. L-692,585 also stimulated an immediate increase in cortisol levels. Transection of the hypophyseal stalk dramatically decreased but did not ablate the GH or cortisol response to L-692,585. Co-administration of L-692,585 + GRF induced an immediate GH response of similar magnitude in the intact and HST animal. We conclude that L-692,585 has a direct but limited action at the level of the pituitary and that an intact hypophyseal stalk is required for a maximal GH and cortisol response. L-692,585 acts with GRF at the level of the pituitary to induce a maximal GH response. These findings suggest that L-692,585 stimulates GH secretion by acting in combination with GRF and interrupting the inhibitory tone of somatostatin on the somatotroph.

Activity of a novel nonpeptidyl growth hormone secretagogue, L-700,653, in swine.

L-700,653 is a potent nonpeptidyl GH secretagogue consisting of a benzolactam structure: (4'-[[3(R)-[[3-[(2(S),3-dihydroxypropyl) amino]3-methyl-1-oxobutyl]amino]2,3,4,5-tetrahydro-2-oxo-1H-1-benzaze pin- 1-yl]methyl][1,1'-biphenyl]2-carboxamide hydrochloride). When administered sc by a Medi-Jector device at 0, 0.003, 0.01, 0.03, and 0.1 mg/kg BW to male castrated swine (approximately 50 kg BW), L-700,653 stimulated dose-related increases in peak plasma GH concentrations by 20% (P = NS), 150% (P = NS), 250% (P < 0.05), and 340% (P < 0.05), respectively, over the saline vehicle control value (11.3 +/- 6.5 ng/ml) and stimulated increases in GH areas under the curve (AUCs) by 10% (P = NS), 30% (P = NS), 90% (P < 0.05), and 100% (P < 0.01), respectively, over the saline vehicle control value (799 +/- 145 ng/min.ml). After sc administration of L-700, 653, there were no significant changes in plasma LH levels. Subcutaneous dose of 0.03 or 0.1 mg/kg increased plasma cortisol AUCs by 60% (P = NS) and 150% (P < 0.03) over the control value (2461 +/- 935 ng/min.ml) and increased cortisol peaks by 80% (P = NS) and 200% (P < 0.01), respectively, over the control value (38.3 +/- 12.3 ng/ml). Repeated sc administration of L-700,653 (0.03 or 0.1 mg/kg) at 0800, 1400, and 2000 h daily over 3 days consistently increased mean GH peak and GH AUC at each treatment period, with minimal and maximal increases of 40% and 190% in GH peak level at the 0.03 mg/kg dose and 100% and 400% increases in GH peak level at the 0.01 mg/kg dose, respectively. Continuous i.v. infusion of L-700,653, at either 0.01 or 0.1 mg/kg BW.h over a 180-min period, increased GH AUCs by 60% (P = NS) or 470% (P < 0.01) and GH peaks by 190% (P = NS) or 1520% (P < 0.01), respectively, over the control value (589 +/- 313 ng/min.ml; 7.0 +/- 11.1 ng/ml). After a 180- to 300-min saline infusion, an iv bolus dose of 0.1 mg/kg L-700,653 resulted in GH responses inversely proportional to the previous infusion dose, i.e. 0, 0.01, or 0.1 mg/kg.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of exogenous growth hormone and diethylstilbestrol on growth and carcass composition of growing lambs.

An 8-wk growth trial was conducted to assess the effects of ovine growth hormone (oGH; 7 mg/d, sc) on growth performance and carcass composition of normal, growing wether lambs. Diethylstilbestrol (DES; .1 mg/d, sc) and control lambs were included for comparisons. Plasma oGH levels at 8 wk were 1.9, 5.5 (P less than .05) and 138.1 ng/ml (P less than .001) for controls, DES and oGH lambs, respectively. Diethylstilbestrol did not increase plasma oGH until the fourth week. The oGH improved feed conversion 7.4% (FC; P less than .05), but did not alter average daily gain (ADG) or feed intake (ADF). Diethylstilbestrol increased ADG 15.3% (P less than .05) and improved FC 16.1% (P less than .01), with no effect on ADF. The primary effect of oGH on carcass composition was to decrease the quantity of fat 8.9% (P less than .05). In addition, oGH may have increased protein 6.5% (P less than .10) and moisture 4.0% (not significant). Diethylstilbestrol increased the quantity of carcass protein 10% (P less than .01) and moisture 8.7% (P less than .05), with no effect on fat. In these studies, the primary effect of exogenous oGH on normal, growing lambs was to reduce carcass fat, which may account for the observed improvement in FC. Diethylstilbestrol, at 1/70th of the oGH dose, was superior to oGH for improving FC (P less than .05) and ADG (P less than .10). Improvements in body weight of the lambs given DES were observed 2 wk before an increase in plasma oGH. In addition, DES, unlike exogenous oGH, did not alter the quantity of carcass fat. These observations do not support the concept that the mode of action of DES is through increased GH secretion.

Thiopeptin for the prevention of ovine lactic acidosis induced by diet change.

Inclusion of thiopeptin, a sulfur-containing peptide antibiotic, at 0, 2.75, 5.5, 8.25, 11 and 22 ppm in the feed was evaluated in 8-week growth trials with 252 lambs. An abrupt diet shift to micronized milo at the start of the trials was used to provide a lactic acidosis challenge. Five of 78 control lambs died within 48 hr after the challenge. In lambs fed diets containing thiopeptin at levels of 11 ppm or more, there was no evidence of lactic acidosis. Lambs given thiopeptin at 11 ppm or more ate 11% more (P less than .05) and gained 20% more (P less than .05) than controls during the 8-week trial. Most of the improvement occurred during the first 2 weeks. Incidence of death was lower among lambs given thiopeptin at 2.75 to 8.25 ppm, but these animals showed no improvement in performance. In another study, abruptly shifting lambs to the micronized milo diet was found to provide an acute lactic acidosis challenge. After the shift, four of eight lambs developed ruminal lactic acidosis, with one dying of systemic lactic acidosis, with one dying of systemic lactic acidosis when plasma lactate exceeded 20 mumoles/ml. In affected lambs, ruminal lactate increased rapidly from an initial level of .2 mumoles/ml to over 130 mumoles/ml within 12 hr of consumption of the milo. Ruminal lactate returned to normal levels of less than 1 mumole/ml by 30 hr in lambs that recovered. High ruminal concentrations of lactate reduced total volatile fatty acids (VFA), and ruminal pH reflected total ruminal acids. Lactic acidosis did not occur in eight lambs after the switch to micronized milo when thiopeptin was included in the feed at 22 ppm. Ruminal lactate was reduced by 68% (P less than .01) and total ruminal VFA increased by 33% (P less than .05) in lambs fed thiopeptin in comparison with average levels in all controls.

Control of wheat-induced lactic acidosis in sheep by thiopeptin and related antibiotics.

Thiopeptin, thiopeptin-like antibiotics and penicillin were shown previously to be highly active in vitro against Streptococcus bovis, the microorganism believed to be responsible for the initiation of ruminal lactic acidosis. The purpose of this work was to determine the efficacy of these antibiotics in preventing lactic acidosis in lambs challenged by intraruminal administration of ground wheat. Lambs, which were fasted and then given ground wheat at 40 g/kg body weight, showed dramatic increases in rumen and plasma lactate over the 30-hr experimental period. Rumen lactate increased from .2 to peak levels of approximately 150 mumoles/ml by 8 to 10 hr after wheat administration. Plasma lactate increased after rumen lactate was elevated and lambs succumbed when plasma levels exceeded 15 mumoles/ml. Ruminal volatile fatty acids were greatly reduced as rumen lactate increased. Over half of the lambs given ground wheat died within 30 hours. Thiopeptin given as a single dose completely prevented lactic acidosis by reducing rumen lactate 80 to 90%. In addition, thiopeptin permitted "normal" rumen fermentation to continue as indicated by a significant increase in volatile fatty acids. The minimum effective dose of thiopeptin to control acute lactic acidosis was .18 mg/kg body weight. Other members of the thiopeptin class, including sulfomycin, sporangiomycin, siomycin and taitomycin, prevented lactic acidosis in a manner similar to thiopeptin. Penicillin, however, inhibited ruminal volatile fatty acid production as well as lactate synthesis. In addition, the effective period for penicillin in the rumen was only 8 to 16 hr, after which lactate fermentation was reestablished. Thus, thiopeptin and thiopeptin-like antibiotics, but not penicillin, appear to provide prophylactic treatment against lactic acidosis in sheep.