Cardiac muscarinic receptor function in rats with cirrhotic cardiomyopathy

The pathogenesis of cirrhotic cardiomyopathy remains unclear. Because ventricular contractility is dependent on the interplay of stimulatory beta-adrenergic and inhibitory muscarinic receptors, we aimed to examine a possible role of muscarinic M2 receptor overactivity in a rat model of cirrhotic cardiomyopathy. Cirrhosis was induced by bile duct ligation (BDL), while controls underwent sham operations. Contractile responses to the muscarinic agonist carbachol were measured in situ in the autonomic-denervated pithed rat and in vitro in isolated ventricular papillary muscles. Ventricular sarcolemmal plasma membranes were isolated by sucrose density gradients, and muscarinic receptor characteristics were studied using 1-[N-methyl-3H]scopolamine (NMS). Membrane adenylyl cyclase activity was tested by a protein binding assay. Maximum first time derivative of peak ventricular systolic pressure (+dP/dt) for sham-operated and cirrhotic rats at baseline was 3,599 +/- 296 versus 1,226 +/- 63 mm Hg/sec (P < .01). Maximum first time derivative of ventricular diastolic relaxation (-dP/dt) for sham and cirrhotic rats at basal levels was -3,040 +/- 235 versus -864 +/- 59 (P < .01). The +dP/dt(max), and -dP/dt(max) responses to carbachol were blunted in the cirrhotic rats. The cirrhotic papillary muscles showed significantly less inhibition to incremental doses of carbachol than control rat muscles. Likewise, isoproterenol-stimulated membrane adenylyl cyclase activity was significantly less inhibited by carbachol doses in the cirrhotic rats. Membrane M2 receptor density and binding affinity in cirrhotic rat hearts were similar to controls. We conclude that muscarinic responsiveness was blunted in cirrhotic hearts, but this was not caused by receptor down-regulation, suggesting changes in postreceptor factors. These changes in muscarinic function are likely compensatory, and M2 receptor overactivity is not involved in the genesis of cirrhotic cardiomyopathy.     

Serotonin-induced constriction of ocular arteries in atherosclerotic monkeys. Implications for ischemic disorders of the retina and optic nerve head

BACKGROUND: Ischemic disorders of the retina and optic nerve head, which constitute a common cause of visual loss, are usually seen in patients with atherosclerosis. OBJECTIVE: To test the hypothesis that serotonin, which is released when platelets aggregate, may produce vasospasm in atherosclerotic monkeys and, thus, may contribute to the ischemic disorders and that short-term dietary treatment of atherosclerosis causes the propensity to vasospasm to subside. METHODS: We studied the response of retinal and posterior ciliary circulation to serotonin in 18 atherosclerotic (25 eyes) and 5 normal (8 eyes) cynomolgus monkeys. The eyes were evaluated by color fundus photography and fluorescein fundus angiography. The eyes were examined under basal conditions and, at a different time, during the intravenous infusion of serotonin. In 6 of the 18 atherosclerotic animals, the evaluation was repeated 5 to 12 months after discontinuing the atherogenic diet (ie, the regression group). RESULTS: Serotonin had no effect in normal monkeys. In 18 atherosclerotic monkeys, serotonin produced transient occlusion or delayed filling of the central retinal artery and/or posterior ciliary artery (PCA) in 9 eyes of 9 animals, involving the central retinal artery in 5, lateral PCA in 8, and medial PCA in 5, in various combinations. In 6 animals (6 eyes) of the regression group, the vasoconstrictor effect of serotonin was abolished completely, except in the medial PCA in 1 eye. CONCLUSIONS: Serotonin, in the presence of atherosclerotic lesions, can cause transient, complete occlusion or impaired blood flow in the central retinal artery and/or PCA. We speculate that this mechanism may play a role in the development of ischemic disorders of the retina and optic nerve head. Discontinuing the atherogenic diet abolished or markedly improved the serotonin-induced vasoconstriction within a few months.     

A mutation causing pseudohypoaldosteronism type 1 identifies a conserved glycine that is involved in the gating of the epithelial sodium channel

Pseudohypoaldosteronism type 1 (PHA-1) is an inherited disease characterized by severe neonatal salt-wasting and caused by mutations in subunits of the amiloride-sensitive epithelial sodium channel (ENaC). A missense mutation (G37S) of the human ENaC beta subunit that causes loss of ENaC function and PHA-1 replaces a glycine that is conserved in the N-terminus of all members of the ENaC gene family. We now report an investigation of the mechanism of channel inactivation by this mutation. Homologous mutations, introduced into alpha, beta or gamma subunits, all significantly reduce macroscopic sodium channel currents recorded in Xenopus laevis oocytes. Quantitative determination of the number of channel molecules present at the cell surface showed no significant differences in surface expression of mutant compared with wild-type channels. Single channel conductances and ion selectivities of the mutant channels were identical to that of wild-type. These results suggest that the decrease in macroscopic Na currents is due to a decrease in channel open probability (P(o)), suggesting that mutations of a conserved glycine in the N-terminus of ENaC subunits change ENaC channel gating, which would explain the disease pathophysiology. Single channel recordings of channels containing the mutant alpha subunit (alphaG95S) directly demonstrate a striking reduction in P(o). We propose that this mutation favors a gating mode characterized by short-open and long-closed times. We suggest that determination of the gating mode of ENaC is a key regulator of channel activity.     

A novel rat homolog of the Saccharomyces cerevisiae ubiquitin-conjugating enzymes UBC4 and UBC5 with distinct biochemical features is induced during spermatogenesis

The Saccharomyces cerevisiae ubiquitin-conjugating enzymes (E2s) UBC4 and UBC5 are essential for degradation of short-lived and abnormal proteins. We previously identified rat cDNAs encoding two E2s with strong sequence similarity to UBC4 and UBC5. These E2 isoforms are widely expressed in rat tissues, consistent with a fundamental cellular function for these E2s. We now report a new isoform, 8A, which despite having >91% amino acid identity with the other isoforms, shows several novel features. Expression of the 8A isoform appears restricted to the testis, is absent in early life, but is induced during puberty. Hypophysectomy reduced expression of the 8A isoform. In situ hybridization studies indicated that 8A mRNA is expressed mainly in round spermatids. Immunoblot analyses showed that 8A protein is found not only in subfractions of germ cells enriched in round spermatids but also in subfractions containing residual bodies extruded from more mature elongated spermatids, indicating that the protein possesses a longer half-life than the mRNA. Unlike all previously identified mammalian and plant homologs of S. cerevisiae UBC4, which possess a basic pI, the 8A isoform is unique in possessing an acidic pI. The small differences in sequence between the 8A isoform and other rat isoforms conferred differences in biochemical function. The 8A isoform was less effective than an isoform with a basic pI or ineffective in conjugating ubiquitin to certain fractions of testis proteins. Thus, although multiple isoforms of a specific E2 may exist to ensure performance of a critical cellular function, our data demonstrate, for the first time, that multiple genes also permit highly specialized regulation of expression of specific isoforms and that subtle differences in E2 primary structure can dictate conjugation of ubiquitin to different subsets of cellular proteins.     

Some patterns of herbicide and growth regulator intake, persistence, and distribution in sugarcane

The concept of NSD has been modified into TDF's by Orton and Ellis and CRE's by Kirk et al. It was aimed to study the variability of these new concepts on the exponents of time and number of fractions. It was found that TDF has larger variation with the exponents compared to that of CRE. The use of CRE and NSD for solving the treatment scheduling problems or for intercomparison of various regimes has been simplified by providing readymade estimation of CRE for various doses/fraction with increasing number of fractions. As there is increasing evidence for the change of exponents J and H, nomograms are presented to determine the CRE for various values of J and H. The variation of decay correction factors with the exponent H is also evaluated and is presented. This will help various radiotherapists to use CRE and the decay correction factors consistent with their clinical findings.     

Penetrating stab wounds of the chest: experience with 200 consecutive cases

The incidence of penetrating wounds of the chest is rising rapidly. Opinions continue to differ on their management. Our experience with 200 consecutive cases of stab wounds of the chest between 1972 and 1975 were reviewed. There were 176 males and 24 females. The average age was 31 years; about two-thirds of the patients were under 30. About 74% presented with hemothorax or hemopneumothorax; 21 presented with pneumothorax. Eleven per cent had associated intra-abdominal injuries. Seventy-nine per cent were successfully treated with tube thoracostomy. About 15% underwent thoracotomy, with three deaths (mortality, 10%); the mortality for cardiac wounds was 16%; overall mortality was 1.5%. The overall complication rate was 5.5%, most occurring in patients with cardiac wounds and associated intra-abdominal injuries. The average period of hospitalization was 6.5 days. Treatment was individualized. Indications for each course of therapy are discussed.