Preservation of renal compensatory growth in uninephrectomized rats by low-dose cyclosporine.

The growth-inhibitory effect of prednisone is a serious drawback to its use in kidney graft recipients. At high doses, cyclosporine also inhibits somatic growth in animals. Furthermore, cyclosporine, in addition to being nephrotoxic in patients, is reported to inhibit compensatory renal growth in uninephrectomized rats. It is unclear whether the latter effect is specific to the kidney. In the present study, we have tested, in the uninephrectomized rat model, the effect of a low dose cyclosporine that is immunosuppressive but does not inhibit somatic growth. Compared with sham operation, uninephrectomy resulted in a significantly greater kidney-to-body weight ratio 2 and 7 days postsurgery. In uninephrectomized rats treated daily with 10 mg/kg cyclosporine s.c., compensatory renal growth was intact. Kidney wet weight, dry weight, and kidney-to-body weight ratios were similar in vehicle and cyclosporine treated, uninephrectomized animals. Similarly, body weight, food consumption, and size of other organs were not adversely affected by the 10 mg/kg/day cyclosporine treatment. Thus, by reducing cyclosporine to levels that are not generally toxic, renal growth is preserved. Our results suggest that the present trend toward using lower doses of cyclosporine in kidney transplant recipients will not only reduce nephrotoxicity, but will also be of benefit in terms of somatic and renal growth, which are important considerations in pediatric transplant patients.

Frog brain and liver show evolutionary conservation of tissue-specific differences among insulin receptors.

The insulin receptors of frog brain and liver show features typical of other insulin receptors with regard to affinity and specificity of binding to insulins and proinsulin, solubility in Triton X-100, binding to and elution from wheat germ agglutinin, and insulin-sensitive tyrosine kinase activity. Likewise, the brain and liver receptors differ from one another in electrophoretic mobility and susceptibility to treatment with neuraminidase, analogous to brain and liver receptors of reptiles, birds, and mammals; while the functional implications of these differences are unknown, their evolutionary conservation for 400-500 million years suggests the possibility that they might have importance.

Insulin receptors in lizard brain and liver: structural and functional studies of alpha and beta subunits demonstrate evolutionary conservation.

Specific insulin receptors are present in the liver and brain of the lizard Anolis carolinesis. In this study, the specific binding of 125I-insulin to the receptors showed time, temperature and pH dependency. Specific binding to crude membranes prepared from brain was 1-2% of the total radioactivity added compared to 4-5% in the crude membranes prepared from liver. Solubilization and wheat germ agglutinin purification of the membranes resulted in an increase in the specific binding (per mg of protein) between 6 and 32 times for liver membranes and 13-186 for brain membranes. Binding inhibition of tracer insulin by unlabeled porcine insulin was characteristic for insulin receptors with 50% inhibition for liver crude membranes at 60 ng/ml of porcine insulin and 0.7 ng/ml for purified brain insulin receptors. Chicken insulin was 2- to 3-fold more potent and proinsulin about 100 times less potent than porcine insulin. The alpha-subunits of liver and brain had apparent molecular weights on sodium dodecyl sulfate polyacrylamide gel electrophoresis of 135 kDa and 120 kDa respectively. Apparent molecular weights of beta subunits were 92 kDa for both tissues. Insulin stimulated phosphorylation of the beta subunit of both brain and liver receptors. Both tissues demonstrated tyrosine-specific phosphorylation, which was stimulated by insulin, of exogenously added artificial substrates. In addition, purified brain insulin receptor preparations contained an endogenous protein with apparent molecular weight of 105 kDa, whose phosphorylation was stimulated by insulin (10(-7) mol/l). This phosphoprotein was not immunoprecipitated by anti-insulin receptor antibodies. These studies suggest that the structural differences between brain and liver receptors previously demonstrated in the rat are also present in the lizard, which is about 300,000,000 years older than the mammalian species. Thus, there is strong evolutionary conservation of the brain insulin receptor.

Plasma cholesterol levels in eviscerated rats.

Eviscerated rat models with a functional liver in which the kidneys or pancreas could be left in situ or removed were used. We found that removal of the gastrointestinal tract leaving the liver and kidneys intact resulted in a significant elevation above normal of the plasma cholesterol. In the absence of the liver, esterified cholesterol is decreased. The presence or absence of the kidneys plays no role here; esterification of cholesterol is primarily a liver function. The elevation in total cholesterol levels after removal of the gastrointestinal tract and pancreas is probably due to a lack of insulin action on peripheral tissues. This elevation in cholesterol is similar to that seen in genetic, surgical and chemical diabetes. Complete restoration of plasma cholesterol patterns to intact animal levels was seen only when the pancreas, liver and kidneys were left functional in the eviscerated rat. These data indicate that in this experimental model the absence of the intestinal tract per se does not significantly modify plasma cholesterol levels and that the critical regulators of cholesterol metabolism appear to be the liver and the endocrine pancreas.

Plasma cholesterol levels in eviscerated rats.

Eviscerated rat models with a functional liver in which the kidneys or pancreas could be left in situ or removed were used. We found that removal of the gastrointestinal tract leaving the liver and kidneys intact resulted in a significant elevation above normal of the plasma cholesterol. In the absence of the liver, esterified cholesterol is decreased. The presence or absence of the kidneys plays no role here; esterification of cholesterol is primarily a liver function. The elevation in total cholesterol levels after removal of the gastrointestinal tract and pancreas is probably due to a lack of insulin action on peripheral tissues. This elevation in cholesterol is similar to that seen in genetic, surgical and chemical diabetes. Complete restoration of plasma cholesterol patterns to intact animal levels was seen only when the pancreas, liver and kidneys were left functional in the eviscerated rat. These data indicate that in this experimental model the absence of the intestinal tract per se does not significantly modify plasma cholesterol levels and that the critical regulators of cholesterol metabolism appear to be the liver and the endocrine pancreas.

Hypotensive response to prostacyclin and 6-keto-PGE1 following hepatectomy in the rat.

Prostacyclin (PGI2) is metabolized to 6-keto-prostaglandin E1 (6-keto-PGE1) which is more stable yet equipotent to PGI2 in lowering systemic arterial blood pressure in the dog. In this study, partial hepatectomy was performed to determine the role of the liver in the vasodepressor response to both intravenously administered PGI2 and 6-keto-PGE1. The magnitude and the duration of systemic hypotensive responses were measured in hepatectomized and sham-operated male Wistar rats following less than maximal, equidepressor doses of PGI2 (0.3 microgram/kg), 6-keto-PGE1 (1.0 microgram/kg), and also PGE1 (3.0 micrograms/kg) and PGE2 (3.0 micrograms/kg). Hepatectomy did not significantly alter the magnitude of the systemic hypotensive response to any of the prostaglandins tested. This indicates that the liver and hepatic circulation do not contribute significantly to the hypotensive effect of these prostaglandins by alterations of systemic vascular resistance, venous pooling of blood, or the generation of additional vasoactive metabolites as may be expected following administration of these prostaglandins. However, hepatectomy did significantly increase the duration of the hypotensive response to PGI2 and 6-keto-PGE1 but not PGE1 or PGE2. We conclude that in vivo, the liver has a more significant role in PGI2 and 6-keto-PGE1 inactivation than in the inactivation of PGE1 and PGE2 when administered intravenously. These results also support the relatively greater significance of the lung in the inactivation of PGE1 and PGE2 in vivo.

Comparison of insulin secretion by the isolated perfused pancreas and perifused islets of the spiny mouse (Acomys cahirinus).

The dynamics of glucose-stimulated insulin release were studied in the perfused pancreas and in isolated perifused islets of spiny mice. The pattern of insulin release induced by an increase of the glucose concentration from 2.8 mM to 16.7 mM was different in the two preparations. In the perfused pancreas there was an early insulin release contrasting with an absence of the early response in isolated islets. The later insulin release response (5 min to 30 min) was present and similar in both preparations. The reduction of early phase insulin release may be due to a reduced glucose sensitivity in the beta cells of spiny mice, most apparent in isolated islets.

Hyperglucagonemia after removal of lower bowel in rats.

Surgical removal of the jejunum, ileum, and colon from rats (LBX) results in greatly elevated levels of plasma immunoreactive glucagon (pIRG) 24 h after surgery (0.98 +/- 0.07 ng/ml, n = 51 vs. 0.20 +/- 0.02 ng/ml, n = 34 in sham-operated controls). Such elevations in pIRG were not noted after gut transection or the removal of ileum, jejunum, or colon alone, ileum plus jejunum, or stomach plus duodenum. Coupled with the failure of adrenal demedullation, adrenalectomy or ganglionic blockade to lower pIRG in LBX animals, these findings suggest that surgical stress alone is an unlikely cause for LBX-induced hyperglucagonemia. It was also shown that alpha-cells in LBX animals retained their responsiveness to both the inhibitory effects of somatostatin and glucose infusion as well as the stimulatory effects of arginine infusion. Chromatography revealed a normal pattern of IRG in the plasma of LBX animals. It is postulated that LBX-induced hyperglucagonemia may result from the removal of an inhibitory factor present in the lower bowel.

Effect of corticosteroids on arachidonate induced mortality in male and female mice.

Sodium arachidonate (50 mg/kg) given intravenously to male and female mice induces pulmonary emboli followed by respiratory distress and cyanosis. Female mice are significantly more resistant to this treatment than male mice. Cortisone pretreatment for four days to intact mice (10 mg/kg/day/4 days) had a significant protective effect in both males and females against arachidonate toxicity, eliminating the sex difference previously observed. Adrenalectomy four days before arachidonate infusion increased the sensitivity to SA and resulted in 100% mortality in both sexes. Pretreatment of adrenalized animals with cortisone significantly reduced to some degree the mortality rate in both sexes. Castration of male and female mice three weeks before adrenalectomy did not affect the mortality rate seen following adrenalectomy alone. In conclusion, exogenous cortical steroids augment the resistance of even intact mice and are absolutely necessary for survival in adrenalectomized animals. The observed sex differences in untreated intact animals is not seen after treatment with cortisone or adrenalectomy.