Intracerebroventricular and intravenous administration of growth hormone secretagogue L-692,585, somatostatin, neuropeptide Y and galanin in pig: dose-dependent effects on growth hormone secretion.

Central regulation of growth hormone (GH) secretion by the GH secretagogue, L-692,585 (585), was determined in Yorkshire barrows (40-45kg BW) with intracerebroventricular (icv) stainless steel cannulas placed by stereotaxic coordinates and indwelling external jugular vein (iv) cannulas for injecting 585 or saline during 3h serial blood sampling. Dose-dependent effects of 585 were determined by icv injections of saline vehicle, 3, 10, and 30microg/kg BW by once daily increment. A switchback study of iv and icv 585 treatment determined central and peripheral regulation of GH secretion by the secretagogue at 30microg/kg BW. When administered icv, 585 increased GH concentration in a dose-dependent manner, with a return to baseline by 60min. GH secretion was attenuated by increased numbers of icv 585 injections (p<0.05); however, it was not affected by increased numbers of iv 585 injections. Icv administration of somatostatin (SRIF) decreased (p<0.05) GH secretion compared with saline-treated controls, and decreased (p<0.05) peak GH response when given in combination with 585 as compared with 585 alone. Porcine galanin (pGAL) modestly increased (p<0.05) GH levels compared with saline controls, but when given icv in combination with 585 peak GH response was lower (p<0.05) compared with 585 alone. Porcine neuropeptide Y (pNPY) administered icv was without effect on GH levels compared with saline controls and decreased (p<0.05) peak GH response when given in combination with 585 as compared with 585 alone. The pharmacological actions by icv administration indicate that the GH secretagogue and neuropeptides act at the level of both porcine pituitary and hypothalamus.

Inhibition of dipeptidyl-peptidase IV does not increase circulating IGF-1 concentrations in growing pigs.

The enzyme dipeptidyl peptidase-IV (DPP-IV) inactivates a variety of bioactive peptides, including glucagon-like peptide-1 (GLP-1) and growth hormone releasing hormone (GHRH). Inhibiting DPP-IV in order to increase circulating GLP-1 is of interest as a treatment for Type II diabetes. Inactivation of DPP-IV may also increase circulating GHRH, potentially enhancing growth in domestic animals. To test the hypothesis that inhibition of DPP-IV activity will influence the growth hormone/ IGF-1 axis, growing pigs (Sus scrofa domesticus, 78 kg) were treated with a DPP-IV inhibitor (Compound 1, the 2,5-difluor-ophenyl analog of the triazolopiperazine MK0431, sitagliptin), and plasma concentrations of IGF-1 were monitored. Pigs were administered either sterile saline (0.11 ml/kg followed by a continuous infusion at 2 ml/hr for 72 hrs, controls, n = 2), Compound 1 (2.78 mg/kg followed by a continuous infusion at 0.327 mg/kg x hr for 72 hrs, n = 4) or GHRH (0.11 ml/kg sterile saline, followed by a continuous infusion of GHRH at 2.5 microg/ kg x hr for 48 hrs, n = 4). Plasma concentrations of Compound 1 were maintained at 1 microM, which resulted in a 90% inhibition of circulating DPP-IV activity. Relative to the predose 24-hr period, area under the IGF-1 concentration curve (AUC) tended to be lower (P = 0.062) with Compound 1 (.79 +/- 130 ng/ml x hr) than controls (543 +/- 330 ng/ml x hr). GHRH treatment increased the IGF-1 AUC (1210 +/- 160 ng/ml x hr, P = 0.049 vs. controls and P = 0.001 vs. Compound 1). We conclude that inhibition of DPP-IV does not alter the circulating levels of IGF-1 in the growing pig.

Research progress in the stimulatory inputs regulating growth hormone (GH) secretion.

A review is presented on progress in the research of stimulatory inputs that regulate growth hormone secretion, including recent results on the action of the hypothalamic peptides growth-hormone releasing factor (GHRH) and pituitary adenylate cyclase-activating polypeptide (PACAP), as well as that of both peptidic (growth hormone-releasing hexapeptide; GHRP-6) and non-peptidyl (L-163,255) synthetic GHSs on somatotrope cell function.

Synthetic growth hormone secretagogues control growth hormone secretion in the chicken at pituitary and hypothalamic levels.

In the chicken growth hormone (GH) secretion is predominantly controlled by two hormones, thyrotropin-releasing hormone (TRH) and somatostatin (SRIH), respectively stimulating and inhibiting GH release. In view of the hypothesis of a novel GH secretagogue (GHS) in mammals, this specific species was used to further assess the exact function of two nonpeptidyl GHSs-L-692,429 and L-163,255. Both synthetic products stimulate GH secretion directly at the level of the pituitary as shown in in vitro perifusion studies. Plasma GH levels increase within 10-15 min after a single challenge of L-692,429 or L-163,255. A SRIH pretreatment dimishes this GH response. Both GH-releasing peptide mimetics decrease hypothalamic TRH concentrations, whereas SRIH levels are not affected. The novel GHS may therefore control GH secretion both at the level of the pituitary and the hypothalamus. The present article shows that nonpeptidyl mimetics also control GH secretion in nonmammalian species suggesting that the endogenous hormone may be a conserved GH stimulator in several vertebrates. The GH response to GHS in birds may be regulated both directly at the level of the pituitary and by releasing another endogenous GH stimulator (TRH) from the hypothalamus.

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.

Comparison of the antisecretory effects of omeprazole when administered intravenously, as acid-stable granules and as an oral paste in horses.

The antisecretory activity of omeprazole on gastric acid when administered i.v., intragastrically or per os, was evaluated in 2 female and 3 castrated male horses. Each horse had been prepared with a chronic indwelling gastric cannula. A single i.v. administration of omeprazole (1.5 mg/kg bwt) was effective in abolishing basal and pentagastrin (PG)-stimulated acid secretion. Once daily, nasogastric administration of omeprazole in acid-stable granules for 5 days inhibited acid secretion in a dose-dependent manner: 57% (1.5 mg/kg bwt) and 98% (5.0 mg/kg bwt) reduction of PG-stimulated acid secretion. The degree of inhibition was maintained over a 19 day treatment period with once daily dosing. A prototype oral paste formulation containing either acid-stable omeprazole granules or uncoated omeprazole powder was equipotent when compared to a similar dosage of acid-stable omeprazole granules administered by nasogastric tube. A dose-dependent inhibition was seen with the oral paste formulation containing omeprazole powder: 55% (1.5 mg/kg bwt) and 77% (3.0 mg/kg bwt) reduction of PG-stimulated acid secretion after 5 days. Therefore, a paste formulation of omeprazole powder may offer an effective, easily administered, once daily acid inhibitory treatment for gastric ulcer disease in horses.

Pituitary and extrapituitary action sites of the novel nonpeptidyl growth hormone (GH) secretagogue L-692,429 in the chicken.

Chickens were used as a model to further analyze the efficacy and specificity of L-692,429, a novel nonpeptidyl mimic of growth hormone (GH)-releasing peptide-6 (GHRP-6), which is a specific GH-releasing secretagogue in mammals. Actions at the level of the pituitary and the hypothalamus were studied. Pituitaries isolated from 1-day-old (C1) chicks responded in a dose-dependent manner to L-692,429 (ED50 = 10 nM). Using equimolar concentrations of thyrotropin-releasing hormone (TRH), human GH-releasing hormone (hGHRH1-29), and L-692,429 (10 nM), L-692,429 had 20-25% the in vitro potency of the two endogenous releasing factors. There was an additive effect between hGHRH1-29 (10 nM) and L-692,429 (10 or 100 nM) on GH release from C1 pituitaries but no such additive effect was observed when pituitaries were exposed to both TRH (10 nM) and L-692,429 (100 nM). An acute challenge with 50 microg L-692,429 resulted in increased plasma GH levels within 5 min, which remained elevated for up to 15 min (C1 chickens). This increase in GH was accompanied by a drop in hypothalamic TRH content by 5 min. Hypothalamic somatostatin (SRIH) content did not change. Plasma corticosterone concentrations were increased following L-692,429 treatment, whereas plasma alpha-subunit, T4, and T3 levels were unchanged. To confirm the role of the decreased hypothalamic TRH concentrations in the GH-releasing activity of L-692,429 in the chicken, chickens (C1) were pretreated with normal rabbit serum (NRS) or a TRH antiserum (1/50) 1 h prior to the L-692,429 challenge. Both groups showed an increase in circulating GH but the increase was within 5 min inhibited by the TRH antiserum pretreatment, whereas no differences were noted in plasma corticosterone levels. It is concluded that in the chicken the GH secretagogue L-692,429 has a dual action site: (1) directly at the level of the pituitary and (2) centrally through an increase in hypothalamic TRH release.

A potent, orally bioavailable benzazepinone growth hormone secretagogue.

The identification of L-739,943 (8b), a potent, orally bioavailable benzolactam growth hormone secretagogue, is obtained from zwitterionic L-692,429 through modification of its amino acid side chain and replacement of the acidic 2'-tetrazole with the neutral and potency enhancing 2'-(N-methylaminocarbonylamino)methyl substituent. L-739,943 is orally active for the release of growth hormone in beagle dogs at doses as low as 0.5 mg/kg. Oral bioavailability in dogs of 8b is 24% at a dose of 2 mg/kg with a mean drug Cmax of 145 +/- 46 ng/mL. L-739,943 represents a significant breakthrough in terms of both potency and oral bioavailability as compared to the prototype benzolactam L-692,429.

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.

Synthesis and biological activities of phenyl piperazine-based peptidomimetic growth hormone secretagogues.

A new class of potent, orally active phenyl piperazine-based GH secretagogues have been discovered from attempts to mimic the arrangement of the phenyl substituent in the spiroindanyl piperidine and spiroindoline sulfonamide privileged structures of 4 and 1, respectively. The best of these compounds, 18 (EC50 = 2.8 nM) is nearly as potent as MK-0677 for releasing GH from rat pituitary cells.

Injuries of young elite female basketball players over a six-year period.

OBJECTIVE: To analyze injuries retrospectively among female basketball players at the Australian Institute of Sport (AIS) from 1990 to 1995 inclusive. DESIGN: The medical records of all the female basketball players on AIS (residential) scholarships were examined, and all injuries were recorded. SETTING: The Sports Medicine Department at the Australian Institute of Sport in Canberra, Australia. PARTICIPANTS: The participants were 49 elite female basketball players, holding full scholarships at the AIS, with an average age of 17.6 years at the time of injury presentation. MAIN OUTCOME MEASURES: Injury presentation according to region involved, nature of injury, and most common specific injuries (diagnoses). RESULTS: A total of 223 injuries were recorded: 139 were acute and 84 were chronic. The regions most frequently injured were the knee (18.8%), ankle (16.6%), lumbar spine (11.7%), and lower legs (10.8%). The most frequent diagnoses were ankle lateral ligament sprain (12.1%), patellar tendinitis (6.7%), lower limb stress fractures (5.4%), finger sprains (4.9%), and mechanical low back pain (4.5%). CONCLUSIONS: There was a high incidence of knee and ankle injury in this group of young elite female basketball players, and stress fractures were not uncommon. The incidence of injury in female basketball players may be increasing. Further research in this area may help reduce the risk of stress fractures and serious ankle and knee injuries.

Effects of omeprazole on healing of naturally-occurring gastric ulcers in thoroughbred racehorses.

Seventeen Thoroughbred horses with moderate to severe gastric ulceration were purchased from a race track within 10 days of racing and were treated once daily with either omeprazole (9 horses) or vehicle (8 horses) and evaluated gastroscopically for ulcer healing. Horses were administered omeprazole (1.5 mg/kg bwt/day) or vehicle by nasogastric tube once daily. Gastroscopic examination was performed on Days 0, 4, 7, 11, 14, 17, 21, 24 and 28, until lesions healed completely. Selected images of gastric lesions were captured by computer at each endoscopic examination, with a measuring caliper included in captured images. The area and perimeter of lesions were measured by computer and healing rates of specific lesions were determined by calculating the rate of linear advance of the margins toward the centre of the lesion. Additionally, the number of days to complete healing of the entire gastric squamous mucosa was compared between treatment groups. Gastric lesions healed at a significantly faster rate in horses receiving omeprazole than in vehicle-treated horses (P < 0.001). Complete healing of the entire stomach occurred in 10-21 days in omeprazole-treated horses, and 14-28 days in 3 of 8 vehicle-treated horses, with the remaining vehicle-treated horses having unhealed lesions on Day 28. In addition, 5 vehicle-treated horses developed new lesions in the squamous epithelial mucosa during the trial; no new lesions were observed in the omeprazole-treated group.

Growth hormone secretagogue increases muscle strength during remobilization after canine hindlimb immobilization.

Twenty-two beagles were divided into two equal groups, and the right hindlimb of each animal was immobilized at 105 degrees of knee flexion by external fixation. After 10 weeks of fixation, the device was removed, allowing free mobility for the following 5 weeks. Each day throughout the 15 weeks, one group received a growth hormone secretagogue (treatment) at a dose of 5 mg/kg, and the other received a lactose placebo (control). At weeks 0, 10, and 15, strength as indicated by maximum isometric extension torque was measured in the right hindlimb, biopsies of the vastus lateralis muscle were taken, and the dogs were weighed. Weekly blood samples were analyzed for insulin-like growth factor-1, blood urea nitrogen, and creatine phosphokinase. Between weeks 0 and 10, tetanic torque declined by about 60% (p < 0.001) in both groups, with no significant difference between the groups (p > 0.7). Between weeks 10 and 15, tetanic torque in the treated group increased by 0.81 Nm; this was significantly greater than the increase of 0.25 Nm in the placebo group (p < 0.05). The diameters of slow (type-1) and fast (type-2) fibers measured from the vastus lateralis muscle followed the same trend. At all time points, fiber diameter correlated strongly with torque; this argues against nonmuscular causes such as nerve injury for strength loss. The mean levels of insulin-like growth factor-1 increased 100% by week 4 in the treated group and remained elevated by about 60% throughout the experiment. Levels of insulin-like growth factor-1 in the placebo group decreased 30% within week 1 and remained depressed throughout the experiment. Our interpretation of these data suggests that the growth hormone secretagogue elevated levels of serum insulin-like growth factor-1, which in turn increased the size and strength of the quadriceps muscle during remobilization. These data may ultimately have therapeutic application to humans during rehabilitation after prolonged inactivity.

Repeat administration of the GH secretagogue MK-0677 increases and maintains elevated IGF-I levels in beagles.

We have reported that MK-0677 is a novel, orally active GH secretagogue that stimulates an immediate and long-lasting increase in serum GH levels in dogs. Significant elevations in IGF-I levels were associated with the increased GH secretion. Cortisol secretion was also increased following MK-0677 administration. In the current study, we determined the effect of repeat oral administration of MK-0677 on GH, IGF-I and cortisol levels; we also investigated if the GH and cortisol responses to MK-0677 are influenced by circulating IGF-I concentrations. Following the initial oral administration of MK-0677, GH secretion (area under the time-response curve (AUC) ng/ml per h) was increased 7.9- to 9.8-fold (1.0 mg/kg), 5.6-fold (0.5 mg/kg) or 3.9-fold (0.25 mg/kg). With repeat MK-0677 administration, the GH response was decreased by 41-77%; GH concentrations remained significantly above control in the 0.5 mg/kg and 1.0 mg/kg groups. Individual beagle GH profiles indicated that the increased GH concentration was associated with an amplified GH pulsatile profile. Serum IGF-I levels were significantly increased over control levels at all dosage levels by 480 min on the first day of MK-0677 administration. With repeated administration, IGF-I levels were increased up to 126% and remained elevated through 14 days, the longest treatment period evaluated. While daily MK-0677 administration appeared to increase IGF-I levels over 24 h, as evidenced by significant increases in the pretreatment IGF-I levels on days 4-14, no such increase was noted with alternate day MK-0677 administration; thus the dosage regimen modulated circulating IGF-I levels. MK-0677 stimulated increases in cortisol secretion (AUC microgram/dl per h) on the first day of treatment. A decreased cortisol response was observed following repeated daily treatment with MK-0677; in contrast, with alternate day treatment, no decrease in cortisol response to MK-0677 occurred. A marked increase in circulating IGF-I concentrations following administration of exogenous GH resulted in a significant decrease in both the GH and cortisol response to MK-0677 compared with control animals. Our findings suggested, therefore, that circulating IGF-I concentrations regulate GH and cortisol response to MK-0677. In summary, chronic oral administration of MK-0677 was associated with significant increases in GH and IGF-I levels that were maintained for the duration of the treatment. The GH profile following MK-0677 administration consisted of episodic increases above control. Compared with day 1, repeated daily treatment with MK-0677 resulted in an attenuated GH response that was associated with an increase in circulating IGF-I levels. The cortisol response was similarly reduced during chronic MK-0677 treatment, suggesting that IGF-I mediated negative feedback on both the GH and cortisol axes. The fact that similar attenuation of the GH and cortisol responses to MK-0677 on day 1 was observed if IGF-I levels were increased by treating animals with exogenous GH suggested that the attenuated response to MK-0677 that occurred during chronic treatment was mediated by increases in IGF-I rather than desensitization to MK-0677. Thus, a regulatory feedback loop apparently prevents hyperstimulation of the GH axis by MK-0677. We conclude that MK-0677 offers the potential of an orally active GH secretagogue that can maintain elevated IGF-I levels when administered chronically.

Injuries to elite rowers over a 10-yr period.

The purpose of this study was to analyze retrospectively all injuries occurring in a population of elite rowers over a 10-yr period to determine their pattern of injury. The medical records of all rowers at the Australian Institute of Sport from 1985 to 1994 inclusive were reviewed and all injuries included. Injuries were categorized according to time, location, cause, and whether acute or chronic. The study found a significant incidence of chest injuries, rib stress fractures, and low back injuries, and a high number of injuries occurring outside specific training. Elite rowers have little risk of major injury, but mild and moderate injuries are common.

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.

Transorbital approach to the porcine pituitary.

A transorbital approach to the pituitary gland is described in domestic swine weighing between 40 and 70 kg. A transpalpebral eye exenteration is performed and the optic canal is enlarged caudally, using a bone drill. An operating microscope is used to improve visualization of the surgical site as the pituitary stalk and anterior pituitary are exposed to the level of the optic chiasm. This approach exposes the pituitary sufficiently to perform either a hypophyseal stalk transection or a hypophysectomy or to implant cannulas for hypothalamic-hypophyseal portal blood sampling. This technique has been performed in more than 50 pigs without major complications. Postoperative recovery has been rapid and uneventful. The transorbital approach is a significant refinement of the frontal craniotomy and cerebral elevation technique previously described in the pig, and results in shortened surgery time, minimal brain manipulation, and greatly decreased morbidity.

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.

Sequence of the dog immunoglobulin alpha and epsilon constant region genes.

The immunoglobulin alpha (IGHAC) and epsilon (IGHEC) germline constant region genes were isolated from a dog liver genomic DNA library. Sequence analysis indicates that the dog IGHEC gene is encoded by four exons spread out over 1.7 kilobases (kb). The IGHAC sequence encompasses 1.5 kb and includes all three constant region coding exons. The complete exon/intron sequence of these genes is described.