Physiological responses of mules on prolonged exposure to high altitude (3 650 m)

Eight healthy male animals were inducted and kept for 2 1/2 years at 3 650 m altitude and subjected to normal work schedules. Physiological measurements viz. heart rate, blood pressure, minute ventilation, oxygen consumption, respiration rate, hemoglobin, packed cell haematocrit volume and eosinophil count were made on these animals at periodic intervals. On acute induction to an altitude of 3 650 m these animals demonstrated a sudden increase in tidal volume, a decrease in Rf and no change in V_E, suggesting a decreased dead space/tidal volume ratio at altitude.However, all these changes stabilised within 3 weeks but on prolongation of stay, the physical state of these animals was adversely affected. The respiratory adjustments occurring on return to sea level appear to be a response to thermal stress. The initial increase in heart rate and blood pressure stabilised by the 2nd week.     

Characterization of gastric mucosal membranes: lipid composition of purified gastric microsomes from pig, rabbit, and frog

The lipid compositions of the gradient-purified gastric microsomal membranes from the fundic mucosa of pig, rabbit, and frog were determined. The total lipid content varied widely. Compared to the rabbit (21.6 ± 0.6 mg/100 mg protein), the pig had about twice as much and the frog about three times as much lipid. The levels of cholesterol were higher in both mammalian species (about 32% of the lipid) compared to frog (23%). Phospholipids accounted for about 45, 54, and 52% of the total microsomal lipids from pig, rabbit, and frog and the molar ratios of cholesterol to phospholipid in the three species were 1.95, 1.6, and 1.17, respectively. Phosphatidyl choline and phosphatidyl ethanolamine together constituted about 75% of the total phospholipids in pig and frog and 93% in rabbit gastric microsomes. Sphingomyelin comprised 19.3, 3.2, and 1.5% in pig, rabbit, and frog, respectively. Phosphatidyl inositol constituted 5, 2.7, and 23.6% in pig, rabbit, and frog, respectively. The ratios of phosphatidyl ethanolamine to phosphatidyl choline were 1.17, 1.1, and 0.85 in pig, rabbit, and frog, respectively. The saturated fatty acids 16:0 and 18:0 and the unsaturated fatty acid 18:1 and 18:2 were the predominant fatty acids in all phospholipids. The ratios of saturated to unsaturated fatty acids were between 0.8 and 0.9 in phosphatidyl choline and 0.27 and 0.5 in phosphatidyl ethanolamine from all three species. The contributions by saturated fatty acids were much more in phosphatidyl inositol and sphingomyelin than in phosphatidyl choline and phosphatidyl ethanolamine from all species. Position 1 of phosphatidyl choline had 63% saturated and 37% unsaturated fatty acids; while the reverse was true for position 2. Phosphatidyl ethanolamine, however, had 85% saturated fatty acids in position 1 compared to only 25% in position 2. Arachidonic acid (20:4) was present in significant amounts in all species located exclusively at position 2 of both phosphatidyl choline and phosphatidyl ethanolamine.     

Bilayer orientation of membrane-bound NH2 groups across microsomal vesicles and their role in the function of gastric K+-stimulated adenosine triphosphatase

The transversal distribution of the free NH₂ groups associated with phosphatidyl ethanolamine and the intrinsic membrane proteins of the purified pig gastric microsomes was quantitated and their relations to the function of the gastric K⁺-stimulated ATPase was investigated. Three different chemical probes such as 2,4,6-trinitrobenzene sulfonic acid (TNBS), 1-fluoro-2,4-dinitrobenzene (FDNB), and 2-methoxy-2,4-diphenyl-3(2H)-furanone (MDPF) were used for the study. The structure-function relationship of the membrane NH₂ groups was studied after modification with the probes under various conditions and relating the inhibition of the K⁺-stimulated ATPase to the ATPase-dependent H⁺ accumulation by the gastric microsomal vesicles. TNBS (2 mm) inhibits nearly completely the K⁺-stimulated ATPase and the vesicular dye accumulation, both in presence and absence of valinomycin plus K⁺. Both the K⁺-ATPase and dye uptake were largely (about 50%) protected against TNBS inhibition if the treatment with TNBS was carried out in presence of 2 mm ATP. TNBS and FDNB labeled 70% of the total microsomal PE; the intra- and extravesicular orientation being 48 and 22%, respectively. The presence or absence of ATP did not have any effect on the TNBS labeling of microsomal PE. ATP, however, significantly (P < 0.05) reduced the labeling of protein-bound NH₂ groups of gastric microsomes by TNBS. The intra- and extravesicular orientation of the protein NH₂ groups were 60 and 40%, respectively. Eighteen percent of the total protein-NH₂ appeared to be associated with the K⁺-stimulated ATPase; the rest being associated with non-ATPase proteins of the microsomes. About half (50%) of the total free NH₂ groups of the K⁺-stimulated ATPase were exposed to the vesicle exterior and were found to play critical roles in gastric ATPase function. The generation of florescence after MDPF conjugation of gastric microsomes was largely (50%) inhibited by ATP. ATP also protected completely the MDPF inhibition of gastric K⁺-stimulated ATPase and dye uptake.     

MECHANISM OF ACTION OF NOTEXIN AND NOTECHIS 11-5 ON SYNAPTOSOMES

The neurochemical activity of notexin and notechis II-5 was investigated using a synaptosomal preparation of rat cerebral cortices. In preparations preincubated with [³H]choline in order to label acetylcholine, the toxins caused a rapid release of the transmitter which was calcium-dependent. The toxins were also potent inhibitors of high affinity choline uptake. Both agents produced a marked depolarization of the synaptosomal preparation as measured by a fluorescent dye and at high concentrations lysed the preparation. At a concentration of 0.1 μM, notexin and notechis II-5 caused a 50% increase in the efflux of lactate dehydrogenase activity. These results, together with electron microscopic observations, indicated that the toxins disrupt the synaptosomal membranes presumably by their inherent phospholipase activity. The release of acetylcholine and inhibition of choline uptake, together with the depolarization of synaptosomal membranes noted in this study, could explain the observed electrophysiological effects of these toxins.     

Lysine production from hydrocarbon by Micrococcus varians 2Fa

A bacterium isolated from Assam (India) soil was found to accumulale l-lysine from hydrocarbon and was identified as a strain of Micrococcus varians. The strain is able to grow and accumulate lysine in a purely synthetic medium though supplementation of the synthetic medium with casamino acids significantly improves the yield. The yield of l-lysine under optimal conditions was found to be 2.6 g X 1(-1) of the compound isolated in crystalline form.     

Effect of selective muscarinic receptor agonists and antagonists on active-avoidance learning acquisition in rats

Effect of some selective muscarinic receptor agonists and antagonists was investigated on learning acquisition in an active-avoidance paradigm in rats which records an anticipatory conditioned avoidance apart from the classical conditioned avoidance response. The muscarinic M1 agonists, arecholine, pilocarpine and McN-A-343, facilitated learning acquisition, which was attenuated by the selective M1 antagonist, pirenzepine. On the other hand, M2 receptor agonist, carbachol, and physostigmine, induced a dose-related dual response, with lower doses retarding and higher doses facilitating the learning acquisition. The former effect was attenuated by gallamine, a muscarinic M2 antagonist, while the latter response was inhibited by pirenzepine, indicating that these putative M2 receptor agonist lose their receptor specificity on dose increment. The selective M2 receptor antagonists, gallamine and AF-DX 116, facilitated learning acquisition, which was inhibited by pirenzepine and the acetylcholine synthesis inhibitor hemicholinium. The results support the cholinergic hypothesis of learning and memory and indicate that M1 receptor agonists and M2 receptor antagonists are likely to prove beneficial in memory deficits. The data also indicates that the clinical dose of some drugs, like physostigmine, needs to be carefully established for optimum therapeutic benefit.     

Effects of muscarinic receptor agonists and antagonists on response of non-extensor rats to maximal electroshock

Rats which do not respond consistently to maximal electroshock by exhibiting the classical hindlimb extensor response, are designated as 'flexors', and can serve as a useful experimental model for investigating seizure mechanisms. 20-25% Charles Foster rats exhibit the flexor status and were used in this study. The flexor rats were converted to extensors by acetylcholine (icv), physostigmine (ip) and the selective muscarinic M1 receptor agonists, arecholine (ip) and McN-A-343 (icv). This conversion of flexors to extensors was significantly attenuated by M1 receptor antagonists scopolamine (ip) and pirenzepine (icv). The M2 receptor agonist, carbachol (icv), had no effect in lower doses but induced conversion of flexor rats to the extensor status only in very high doses which may be due to loss of receptor specificity on dose increment. The M2 receptor antagonists, gallamine (icv) and AF-DX 116 (ip), also induced significant conversion of flexors to extensors, which was dependent upon the availability of neuronal acetylcholine since the effects were attenuated following pretreatment with hemicholinium, an inhibitor of acetylcholine synthesis. The results suggest that the central cholinergic system has a facilitatory pro-convulsant effect, mediated through the muscarinic M1 receptors, an action modulated by the M2 receptors.     

Effects of Hypoxia on the Activity of the Dopaminergic Neuron System in the Rat Striatum as Studied by In Vivo Brain Microdialysis

The purpose of the present study is to clarify the effects of hypoxia on the activity of the dopaminergic neurons in the brain and its mechanism of action. For this purpose, the effects of hypoxia on the extracellular levels of 3,4-dihy-droxyphenylethylamine (dopamine) were examined in the rat Striatum using in vivo brain microdialysis in the presence or absence of pretreatment with either tetrodotoxin (a blocker of voltage-dependent sodium channels) or nomifensine (a blocker of dopamine reuptake). Exposure to various degrees of hypoxia (15, 10, and 8% O₂ in N₂) increased dopamine levels in striatal dialysates to 200, 400, and 1,100%, respectively, of the control value. On reoxygenation, dopamine levels in the dialysates rapidly returned to the control level. Reexposure to hypoxia increased the dopamine levels to the same extent as during the first exposure. After addition of tetrodotoxin (40 mUM) to the perfusion fluid or pretreatment with nomifensine (100 mg/kg, i.p.), exposure to hypoxia no longer increased the dopamine levels. These results suggest that although hypoxia induces an increase in the extracellular dopamine levels (hence, an apparent increase in the activity of the dopaminergic neurons), this increase is not the result of an increase in dopamine release itself, but rather the result of inhibition of the dopamine reuptake mechanism.     

Receptor-operated calcium-channels in isolated rabbit jejunum.

Calcium channels were studied in isolated spontaneously rhythmic rabbit jejunum using the muscarinic agonist carbachol as stimulant. Carbachol failed to produce the characteristic phasic and tonic components of smooth muscle contractions. A variety of chemically distinct calcium antagonists, viz. bepridil, diltiazem, isradipine (PN 200-110), nifedipine, and verapamil, non-competitively inhibited the contractions. Diltiazem was most potent (-logIC50 = 8.30) and bepridil least potent (-logIC50 = 6.19) in inhibiting the contractions. The findings conclude with the presence of pharmacologically distinct receptor-operated calcium-channels, besides the potential-dependent calcium-channels, in the rabbit jejunum.