Adrenocortical responses to corticotropin-releasing factor in the rat

The time course of plasma corticosterone was measured in male Sprague-Dawley rats whose endogenous release of ACTH had been blocked following rapid i.v. injections of doses ranging from 0.003 to 10 micrograms corticotropin-releasing factor (CRF) per rat and during i.v. infusions at rates ranging from 0.001 to 20 ng CRF X min-1 X 100 g body weight-1. The range of the dose-response curve, following rapid injection, extends from 0.01 to 0.37 micrograms CRF, whereas it extends over a 20 000-fold range from 0.001 to 20 ng CRF X min-1 X 100 g body weight-1 during a continuous infusion. The delayed response to a small rate of CRF could be ascribed to a relatively long time of residence of CRF in the plasma which implies that a relatively long period of time is required until a minimal plasma CRF concentration is reached after the onset of a continuous infusion of CRF at a small rate. When presented with a prolonged infusion of CRF at a large rate, the pituitary secretion of ACTH is rapidly turned on at a rate which exhibits the characteristics of a prolonged secretion at a constant large magnitude.     

Dopamine production by the isolated perfused rat kidney

We used isolated perfused rat kidneys to examine dopamine (DA) production and its relation to renal function. Both innervated and chronically surgically denervated kidneys perfused with a solution containing neither albumin nor tyrosine, excreted 0.2 +/- 0.1 ng DA X min-1 X g wet weight-1 during the 10-min collection period between 30 and 40 min after starting perfusion. When perfused with 6.7% albumin, without tyrosine, innervated kidneys excreted 1.0 +/- 0.06 ng DA X min-1 X g-1 and denervated kidneys excreted 1.0 +/- 0.07 DA X min-1 X g-1. When 0.03 mM tyrosine was included in the albumin perfusate, innervated kidneys excreted 1.2 +/- 0.1 ng DA X min-1 X g-1 (p less than 0.1). Under these conditions DA excretion continued for at least 100 min at which time it was 0.6 ng X min-1 X g-1 and 86 ng/g kidney weight had been excreted. Denervated kidneys perfused with albumin + tyrosine excreted 0.9 +/- 0.13 ng DA X min-1 X g-1. Renal stores of free DA, conjugated DA, and dihydroxyphenylalanine (DOPA) could have provided at the most 30 ng/g of DA. Carbidopa inhibited DA excretion completely. DA excretion did not correlate with renal vascular resistance, inulin clearance, or fractional sodium excretion. In summary, nonneural tissue in isolated perfused kidneys produced DA at the same rate as denervated kidneys in vivo. Less than one-third of the DA produced by isolated kidneys could have come from intrarenal stores of DOPA, free DA, and conjugated DA; the rest was synthesized from unknown precursors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cerebral blood flow in intoxicated newborn piglets

Ethanol exposure in the neonatal period causes impaired brain growth and altered adult behaviour in rats. One possible mechanism may be altered cerebral perfusion caused by ethanol intoxication. We assessed the effects of ethanol on cerebral blood flow and its autoregulation in 2-day-old piglets. Piglets received ethanol (1.4 g/kg) or an equivalent volume of dextrose 5% in water over 30 min. One hour later, cerebral blood flow was measured using the microsphere technique at resting, elevated, and decreased mean arterial blood pressure. Ethanol-treated piglets had total cerebral blood flows of 88 +/- 14, 82 +/- 10, and 82 +/- 12 mL X 100 g-1 X min-1 (mean +/- SE) at mean arterial blood pressures of 12.4 +/- 1.1, 15.7 +/- 1.5, and 8.2 +/- 0.9 kPa. Corresponding values in control piglets were 82 +/- 14, 78 +/- 4, and 82 +/- 7 mL X 100 g-1 X min-1 at mean arterial blood pressures of 10.5 +/- 1.5, 14.0 +/- 1.2, and 7.7 +/- 1.1 kPa. At resting arterial blood pressures, regional blood flows to basal ganglia, cortex, brainstem, and cerebellum in ethanol-treated piglets were 123 +/- 21, 90 +/- 16, 94 +/- 17, and 77 +/- 12 mL X 100 g-1 X min-1, respectively. Corresponding regional blood flows for the control piglets were 118 +/- 16, 85 +/- 15, 76 +/- 16, and 76 +/- 16 mL X 100 g-1 X min-1. Blood flow to basal ganglia was greater than to other brain regions in both ethanol-treated and control piglets (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of oral propranolol and exercise protocol on indices of aerobic function in normal man

The exercise responses to two different progressive, upright cycle ergometer tests were studied in nine healthy, young subjects either with no drug (ND) or following 48 h or oral propranolol (P) (40 mg q.i.d.). The ergometer tests increased work rate by 30 W either every 30 s or every 4 min. Propranolol caused a significant (p less than 0.05) reduction in peak oxygen uptake (VO2) during both the 30-s and 4-min tests (30-s ND, 3949 +/- 718 mL X min-1 (means +/- SD); 30-s P, 3408 +/- 778 mL X min-1; 4-min ND, 4058 +/- 409 mL X min-1; 4-min P, 3725 +/- 573 mL X min-1). There was no difference between 30-s ND and 4-min ND for peak VO2. The ventilatory anaerobic threshold was not significantly different between any test (30-s ND, 2337 +/- 434 mL O2 X min-1; 30-s P, 2174 +/- 406 mL O2 X min-1; ND, 2433 +/- 685 mL O2 X min-1; 4-min P, 2296 +/- 604 mL O2 X min-1). The VO2 at which blood lactate had increased by 0.5 mM above resting levels was significantly lower than the ventilatory anaerobic threshold for the 4-min ND (1917 +/- 489) and the 4-min P (1978 +/- 412) tests, but was not different for the 30-s ND and 30-s P tests. At exhaustion in the progressive tests, the blood PCO2 was higher (p less than 0.05) in both 30-s tests than 4-min tests.(ABSTRACT TRUNCATED AT 250 WORDS)     

Secretory bursts of growth hormone secretion in the dog may be initiated by somatostatin withdrawal

In 28 6-h experiments on 10 conscious resting trained male dogs, plasma growth hormone (GH) was determined at 5-min intervals by radioimmunoassay. For all experiments, the basal GH concentration in plasma was 0.80 +/- 0.06 ng mL-1. In each experiment, 1-3 secretory bursts of GH occurred, raising plasma GH 2.4 to 15.3 times basal concentrations (for all 43 bursts, 6.6 +/- 0.4 times the basal value). Metabolic clearance rates (MCR) and apparent distribution volumes (V) were determined, using stepwise infusions of canine GH. The MCR (3.99 +/- 0.30 mL kg-1 min-1) and V (57.9 +/- 5.5 mL kg-1) were used to transform the GH concentration versus time data into GH secretion rates, using a single compartment approach. Basal GH secretion rates for all 28 experiments were 3.12 +/- 0.24 ng kg-1 min-1. The secretory bursts yield peak GH secretion rates of 9.4 +/- 0.8 times basal secretion and these steep-sloped bursts last 25.1 +/- 1.2 min. Six-hour infusions of 0.15 microgram kg-1 min-1 of somatostatin (SRIF) abolished all secretory bursts but did not lower basal secretion rates. In five of seven SRIF infusion experiments in which samples were taken after the infusion ceased a secretory burst was seen in the hour following cessation of infusion (in four cases within 10 min). These secretory bursts lasted 23.0 +/- 2.9 min and were similar to those seen in control experiments. Infusions of SRIF at 0.05 microgram kg-1 min-1 had no effect. These results imply that during basal GH secretion, a surfeit of SRIF impinges on the somatotrophs, as extra SRIF does not further lower basal secretion. However, during secretory bursts, very little SRIF must be present, as exogenous SRIF blocks these bursts. The bursts are similar in duration to overshoots provoked in perifused dispersed rat somatotrophs by removal of an SRIF signal. It seems likely that their cause in vivo is similar. (All values are means +/- SEM.)     

Angiotensin II increases ACTH release in the absence of endogenous arginine-vasopressin

Recent studies from our laboratory indicate a primary central site of action of Angiotensin II (AII) to release ACTH. The present studies were designed to test whether AII is able to release ACTH in vivo in a similar fashion in intact, cannulated, freely moving Long-Evans (LE) or in vasopressin (AVP)-deficient, Brattleboro (DI) female rats. The in vivo response to AII was compared with that elicited by synthetic CRF. AII injected i.v. (0.4 or 2 micrograms/100 g BW) induced a significant, dose-related increase in plasma ACTH values 5 and 15 min after injection, in both LE and DI rats. CRF given to LE and DI rats at 0.4 micrograms/100 g BW elicited a larger increase in ACTH plasma values than a similar dose of AII, 5 or 15 min after the injection. Moreover, ACTH levels after CRF in DI rats were significantly greater than those obtained in LE controls. In vitro studies using dispersed anterior pituitary cells indicate that the response of cells from either LE or DI rats to AII or AVP (both at 10(-9) and 10(-8)M) was similar. Cells from DI donors were hyperresponsive to CRF (2 X 10(-11) and 10(-10)M) in terms of ACTH release when compared with the response of cells from LE rats. The present results suggest that the presence of AVP is not essential to mediate the central response to AII and that AII may act centrally to stimulate CRF release from the hypothalamus in vivo, which would then enhance ACTH output. The results in the DI rat indicate that the increased response to CRF may be an important compensatory mechanism involved in the regulation of adrenocortical function in the DI rat.     

Effect of synthetic ovine corticotropin-releasing factor on growth hormone secretion in patients with acromegaly

In a significant proportion of patients with acromegaly, a non-specific increase in plasma growth hormone (GH) has been recognized following administration of thyrotropin-releasing hormone (TRH) or luteinizing hormone-releasing hormone (LH-RH), probably due to the lack of the specificity of the receptor in their tumor cells. In this study, the effects of corticotropin-releasing factor (CRF), a newly isolated hypothalamic hormone, in addition to TRH and LH-RH, on plasma levels of GH and the other anterior pituitary hormones were evaluated in 6 patients with acromegaly. Synthetic ovine CRF (1.0 microgram/kg), TRH (500 micrograms) or LH-RH (100 micrograms) was given as an iv bolus injection, in the morning after an overnight fast. Blood specimens were taken before and after injection at intervals up to 120 min, and plasma GH, adrenocorticotropin (ACTH), thyrotropin, prolactin, luteinizing hormone, follicle-stimulating hormone and cortisol were assayed by radioimmunoassays. A non-specific rise in plasma GH was demonstrated following injection of TRH and LH-RH, in 5 of 6 and 2 of 5 patients, respectively. In all subjects, rapid rises were observed in both plasma ACTH (34.3 +/- 6.2 pg/ml at 0 min to 79.5 +/- 9.5 pg/ml at 30 min, mean +/- SEM) and cortisol level (9.1 +/- 1.3 micrograms/dl at 0 min to 23.4 +/- 1.2 micrograms/dl at 90 min). However, plasma levels of GH and the other anterior pituitary hormones did not change significantly after CRF injection. These results indicate that CRF specifically stimulates ACTH secretion and any non-specific response of GH to CRF appears to be an infrequent phenomenon in this disorder.     

Total and free testosterone in plasma of hypo- and agonadal men.

Plasma total testosterone (T), apparently free T and testosterone binding globulin (TeBG) capacity determined in 14 normal men aged 30-40 years were 461 +/- 100 ng/100 ml, 9.4 +/- 3.0 ng/100 ml and 5.7 +/- 1.9 X 10(-8) M, respectively, whereas in 16 hypogonadal men the corresponding values were 38.6 +/- 27.2 ng/100 ml, 0.47 +/- 0.41 ng/100 ml and 10.4 +/- 3.4 X 10(-8) M showing the TeBG capacity significantly higher (p less than 0.001) in hypogonadal than in normal men. Treatment of 5 hypogonadal subjects with 250 mg testosterone enanthate plus 50 mg testosterone propionate decreased (p less than 0.001) the TeBG level from 14.7 +/- 2.5 X 10(-8YM to 8.3 +/- 1.4 X 10(-8) M on day 8 after a single injection. According to this difference in TeBG, the free T fraction in plasma rose from 0.94% to 1.9% of the total T concentration. These results suggest that alteration of total plasma T affected the TeBG capacity. Decreased T levels raised and increased T concentrations suppressed TeBG, but with a delayed response to the changed T concentrations. The initial mean values in 12 patients with prostatic cancer aged 60-74 years were 397 +/- 165 ng/100 ml, 4.05 +/- 1.8 ng/100 ml and 11.9 +/- 3.3 X 10(-8) M, respectively. The TeBG capacity in these patients was significantly higher and the free T concentration significantly lower (p less than 0.001) than those of the younger normal males. After treatment with 12 g diethylstilbestrol diphosphate and orchidectomy, the TeBG increased to 33.3 +/- 13.1 X 10(-8) M and the plasma free T concentration decreased to the minimal value of 0.053 +/- 0.04 ng/100 ml.     

Failure of hyperketonemia to alter basal and insulin-mediated glucose metabolism in man

The effect of physiologic elevations of plasma hydroxybutyrate induced by the infusion of sodium D,L-beta-hydroxybutyrate (15 mumol X kg-1 X min-1) on carbohydrate metabolism was examined with the euglycemic insulin clamp technique in nine healthy volunteers. Plasma insulin concentration was acutely raised and maintained at 126 +/- 6 microU/ml and plasma glucose was held constant at the fasting level by a variable glucose infusion. Glucose uptake of 6.53 +/- 0.80 mg X kg-1 X min-1 was unchanged by hyperketonemia when compared with an intraindividual control study using saline instead of beta-OH-butyrate infusion (6.26 +/- 0.59 mg X kg-1 X min-1). In studies, in which the degree of metabolic alkalosis accompanying butyrate infusion was mimicked by the continuous administration of bicarbonate, glucose uptake was also unaffected (6.25 +/- 0.45 mg X kg-1 X min-1). Furthermore, hyperketonemia had no effect on basal glucose production or the suppression of hepatic glucose production following hyperinsulinemia. It is concluded that moderate elevations in plasma beta-hydroxy-butyrate do not alter hepatic or peripheral glucose metabolism.     

Control of right atrial pressure at constant cardiac output suppresses volume natriuresis in anesthetized rats

The blood volume of anesthetized rats was expanded acutely by 33% with donor blood while a caval snare was gradually tightened so that right atrial pressure (RAP) was prevented from rising (n = 6). In control experiments (n = 5) an aortic snare was used to hold mean arterial blood pressure near the values found in the experimental series. However, RAP was allowed to change freely and increased by 1.6 +/- 0.4 mmHg (1 mmHg = 133.322 Pa) during volume expansion. When the two groups were compared, there were no significant differences between their mean arterial blood pressures (near 110 mmHg) or in their cardiac outputs (near 0.25 mL X min-1 X g body weight-1). There were, however, significant differences between their renal responses to the volume load. When RAP was free to change, the rate of volume excretion (V) increased to 30 +/- 15 (SEM) microL X min-1 X g kidney weight-1 (KW) from its control value of 3.49 +/- 0.31 and the rate of sodium excretion (UNaV) increased to 3.59 +/- 0.20 muequiv X min-1 X g KW-1 from its preinfusion value of 0.42 +/- 0.10. When RAP was not allowed to increase during volume loading, V and UNaV did not change from their respective preinfusion values (2.99 +/- 0.46 microL X min-1 X g KW-1 and 0.35 +/- 0.10 muequiv X min-1 X g KW-1). The results imply that during acute blood volume expansion increased central vascular pressure is a prerequisite for the homeostasis of body water and salt.     

Stimulation of the hypothalamic-pituitary-adrenal axis by epidermal growth factor

The effects of mouse epidermal growth factor (mEGF) on the hypothalamic-pituitary-adrenocortical axis were studied in vivo in conscious male rats and in vitro with cultured anterior pituitary cells. Both intravenous (i.v.) and intracerebroventricular (i.c.v.) injections of mEGF (5-20 ng: 8.3-33.3 pmol) produced significant, dose-related increases in plasma ACTH and corticosterone concentrations. The potency of mEGF is 1/20-1/50 of that of rat corticotropin-releasing factor (rCRF), and pretreatment with 150 micrograms alpha-helical CRF (9-41) completely abolished the effects of the two peptides. mEGF in concentrations ranging from 10 pM to 10 nM did not significantly affect ACTH release from dispersed anterior pituitary cells. It also failed to alter ACTH secretion in response to rCRF. These results indicate that mEGF stimulates the pituitary-adrenocortical axis through a CRF-dependent mechanism.     

Effect of furegrelate on renal plasma flow after angiotensin II infusion

We had previously shown that selective thromboxane synthetase inhibition with furegrelate increases urinary excretion of 6-ketoPGF1 alpha, the hydrolysis product of prostacyclin after stimulation of renal prostaglandin synthesis with furosemide. The present study assessed the functional significance of this "redirection" of prostaglandin formation using a more physiologic stimulus, angiotensin II. Sprague-Dawley rats (n = 27) were fitted with a transabdominal bladder cannula. Five days later they were given angiotensin II (10 mg.kg-1.min-1) by intravenous infusion. After 30 min, an infusion of furegrelate, 2 mg/kg, then 2 mg.kg-1.h-1, (n = 9); indomethacin, 2 mg/kg, then 2 mg.kg-1.h-1 (n = 9); or vehicle, 250 microL, then 0.018 mL/min (n = 9) was begun for 60 min. Clearance of [14C]para-aminohippuric acid was taken as a measure of renal plasma flow. Angiotensin II raised the mean arterial pressure in all groups. Administration of furegrelate or indomethacin did not change mean arterial pressure or heart rate. Angiotensin II reduced [14C]p-aminohippuric acid clearance by about 32% (1.42 +/- 0.18 to 0.97 +/- 0.07 mL.min-1.100 g-1, p less than 0.05). Furegrelate attenuated this renal vasoconstriction (0.97 +/- 0.07 to 1.38 +/- 0.17 mL.min-1.100 g-1, p less than 0.05), while indomethacin increased it by a further 32% (1.78 +/- 0.12 to 1.20 +/- 0.12 mL.min-1.100 g-1, p less than 0.05). Vehicle alone had no effect. Furegrelate reduced serum thromboxane B2 by 90% (6.52 +/- 0.030 to 0.7 +/- 0.21 ng/100 microL, p less than 0.05), while indomethacin reduced it by 73% (5.9 +/- 0.99 to 1.4 +/- 0.20 ng/100 microL, p less than 0.05). We conclude that furegrelate attenuates the renal vasoconstriction of angiotensin II, presumably by enhancing the formation of vasodilator prostaglandins.     

Simultaneous diffusion of inositol and mannitol in the rat brain

The diffusion of both inositol and mannitol has been determined simultaneously by the integral bolus method in rat brain. The permeability constant (Kin) of inositol averaged 0.27 +/- 0.02 ml X (100 g)-1 X min-1 or 4 X 10(-7) cm X s-1 at a cerebral capillary surface area of 100 cm2 x g-1. The permeability of mannitol was 0.08 +/- 0.01 ml X (100 g)-1. min-1 or 1 X 10(-7) cm X s-1. Neither glucose nor galactose affected the inositol permeability. Hypoglycemia increased somewhat the Km value for mannitol. The basal ganglia showed an increase Km for both substrates as compared with those obtained for cortex, temporal and parietal tissues.     

Stimulation of prolactin secretion by L-3,4-dihydroxyphenyl-serine (L-DOPS) via central norepinephrine in the rat

Intracerebroventricular (icv) injection of L-3,4-dihydroxyphenylserine (L-DOPS) (50 and 250 micrograms/rat) raised in a dose-related manner both plasma prolactin (PRL) and CSF norepinephrine (NE) in urethane-anesthetized male rats. Intravenous (iv) injection of larger doses of L-DOPS (5 and 10 mg/100 g BW) slightly but significantly increased plasma PRL and CSF NE. L-DOPS injection (50 micrograms/rat, icv or 5 mg/100 g BW, iv) also raised plasma PRL in conscious rats. There was a good correlation (r = 0.74) between CSF NE and peak plasma PRL in the anesthetized animals. Propranolol (100 micrograms/100 g BW, iv) inhibited plasma PRL responses to L-DOPS (50 micrograms/rat, icv) and NE injection (1 microgram/rat, icv) raised plasma PRL in anesthetized animals. These findings indicate that L-DOPS stimulates PRL secretion via central noradrenergic mechanisms in the rat.     

Ability of cortisol and progesterone to mediate the stimulatory effect of adrenocorticotropic hormone upon testosterone production by the porcine testis

The influence of corticosteroids and progesterone upon porcine testicular testosterone production was investigated by administration of exogenous adrenocorticotropic hormone (ACTH), cortisol and progesterone, and by applying a specific stressor. Synthetic ACTH (10 micrograms/kg BW) increased (P less than 0.01) peripheral concentrations of testosterone to peak levels of 5.58 +/- 0.74 ng/ml by 90 min but had no effect upon levels of luteinizing hormone (LH). Concentrations of corticosteroids and progesterone also increased (P less than 0.01) to peak levels of 162.26 +/- 25.61 and 8.49 +/- 1.00 ng/ml by 135 and 90 min, respectively. Exogenous cortisol (1.5 mg X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although peripheral concentrations of corticosteroids were elevated (P less than 0.01) to peak levels of 263.57 +/- 35.03 ng/ml by 10 min after first injection. Exogenous progesterone (50 micrograms X three doses every 5 min) had no effect upon circulating levels of either testosterone or LH, although concentrations of progesterone were elevated (P less than 0.01) to peak levels of 17.17 +/- 1.5 ng/ml by 15 min after first injection. Application of an acute stressor for 5 min increased (P less than 0.05) concentrations of corticosteroids and progesterone to peak levels of 121.32 +/- 12.63 and 1.87 +/- 0.29 ng/ml by 10 and 15 min, respectively. However, concentrations of testosterone were not significantly affected (P greater than 0.10). These results indicate that the increase in testicular testosterone production which occurs in boars following ACTH administration is not mediated by either cortisol or progesterone.     

Structure-activity studies on 4-substituted-2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists

Structure-activity studies around the 4-position of 2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists suggest that there is a large lipophilic cavity in the rat CRF receptor, which can accommodate a wide variety of substituents at this position in contrast to the steric constraints observed for other positions on the 2-anilinopyrimidine core. The chemical syntheses and biological activities of 2-anilinopyrimidine CRF antagonists with carbon-linked substituents at the 4-position are reported. Significant improvements in rat pharmacokinetic parameters were achieved relative to those for the lead structure. While the lead compound 1 (rCRF Ki = 44 nM) afforded no detectable rat plasma levels after intraperitoneal (i.p.) or oral (p.o.) dosing, compounds 3-3 (rCRF Ki = 16 nM) and 3-4 (rCRF Ki 59 nM) gave high rat plasma levels at 30 mg/kg (i.p., p.o.) (Cmax = 1389 nM and 8581 nM (i.p.) respectively; Cmax = 113 nM and 988 nM (p.o.), respectively). Furthermore 3-3 and 3-4 had superior bioavailabilities at these doses (59 and 46% (i.p.), respectively; 2 and 10%, (p.o.), respectively).     

Development of a selective photoactivatable antagonist for corticotropin-releasing factor receptor, type 2 (CRF2).

A novel photoactivatable analog of antisauvagine-30 (aSvg-30), a specific antagonist for corticotropin-releasing factor (CRF) receptor, type 2 (CRF2), has been synthesized and characterized. The N-terminal amino-acid d-Phe in aSvg-30 [d-Phe11,His12]Svg(11-40) was replaced by a phenyldiazirine, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl (ATB) residue. The photoactivatable aSvg-30 analog ATB-[His12]Svg was tested for its ability to displace [125I-Tyr0]oCRF or [125I-Tyr0]Svg from membrane homogenates of human embryonic kidney (HEK) 293 cells stably transfected with cDNA coding for rat CRF receptor, type 1 (rCRF1) or mouse CRF receptor, type 2beta (mCRF2beta). Furthermore, the ability of ATB-[His12]Svg(12-40) to inhibit oCRF- or Svg-stimulated cAMP production of transfected HEK 293 cells expressing either rCRF1 (HEK-rCRF1 cells) or mCRF2beta (HEK-mCRF2beta cells) was determined. Unlike astressin and photo astressin, ATB-[His12]Svg(12-40) showed high selective binding to mCRF2beta (Ki = 3.1 +/- 0.2 nm) but not the rCRF1 receptor (Ki = 142.5 +/- 22.3 nm) and decreased Svg-stimulated cAMP activity in mCRF2beta-expressing cells in a similar fashion as aSvg-30. A 66-kDa protein was identified by SDS/PAGE, when the radioactively iodinated analog of ATB-[His12]Svg(12-40) was covalently linked to mCRF2beta receptor. The specificity of the photoactivatable 125I-labeled CRF2beta antagonist was demonstrated with SDS/PAGE by the finding that this analog could be displaced from the receptor by antisauvagine-30, but not other unrelated peptides such as vasoactive intestinal peptide (VIP).     

Glucagon kinetics in growing rats fed different levels of protein and/or energy

The present work was carried out to evaluate the kinetic parameters of glucagon in growing rats divided into three groups: T, H and E. Group T (Control group) was fed a control diet (crude protein: 11.8%). Groups H and E received a high protein diet (crude protein: 19%) distributed in either equal (Group H) or restricted amounts (Group E) with respect to the control. Thus, the main characteristic of Group H was the high level of protein intake (+ 68%) when Group E rats underwent a moderate increase in protein intake but a striking caloric deprivation (-25%). In all cases, the animals were fed a meal every 4 hours. The kinetic parameters of glucagon metabolism were estimated from the plasma disappearance curves of 125I-glucagon for five minutes following a pulse injection of purified 125I-glucagon (1 muCi, about 3.8 ng/100 g BW). Plasma 125I-glucagon was measured after gel filtration of plasma on Biogel P-10. Tissue radioactivity (mainly liver and kidneys) was recorded seven minutes after 125I-glucagon injection. The results showed that the plasma 125I-glucagon level was higher in Group H than in the other groups 1 min after the injection. At all other times (2, 3.5 and 5 min) it was similar in all groups. 125I-glucagon was rapidly cleared from plasma and rapidly taken up by the liver and kidneys. In the 3 experimental groups, mean half-life and metabolic clearance rate were estimated to be 2 min and 6 ml/min/100 g BW, respectively. Excess protein intake resulted in a reduction in the apparent initial distribution volume of 125I-glucagon without modifying significantly its turn-over rate and metabolic clearance rate. Kidneys and liver (6% BW) accounted for about 20% of the 125I-glucagon uptake by tissues 7 min after injection. Group H kidneys and liver were more labelled than in other groups. These results suggest that increased protein intake (without further caloric deprivation) can induce some changes in glucagon metabolism which could partially contribute to the increase in glucagonemia usually observed in animals fed high protein diets.     

Three months energy restricted diet does not reduce peripheral insulin resistance in newly diagnosed non insulin dependent diabetics

Sixteen newly diagnosed non insulin dependent diabetic patients were treated for 3 months with an individual energy restricted diet. The effect on weight, hyperglycaemia and insulin response to oral glucose was measured in all subjects, and in 7, peripheral insulin resistance was estimated using a hyperinsulinaemic glucose clamp at two insulin infusion rates (40 and 400 mU m-2 X min-1). After diet, fasting plasma glucose fell from 12.0 +/- 0.7 mmol/l (mean +/- SEM) to 7.4 +/- 0.5 mmol/l (P less than 0.001) and weight fell from 92.9 +/- 4.2 kg to 85.0 +/- 3.1 kg (P less than 0.001). The plasma insulin response to oral glucose was unchanged after diet therapy. Insulin induced glucose disposal (M) was also unaffected by diet at insulin infusion rates of 40 mU m-2 X min-1 (12.5 +/- 1.5 mumol X kg-1 X min-1 vs 15.7 +/- 1.6 mumol X kg-1 X min-1) and 400 mU m-2 X min-1 (49.5 +/- 2.7 mumol X kg-1 X min-1 vs 55.1 +/- 2.5 mumol X kg-1 X min-1). These results show that 3 months reduction of energy consumption with weight loss in newly diagnosed non insulin dependent diabetics improves B-cell responsiveness to glucose but has no effect on liver glucose output or on peripheral insulin action.