The role of cellular Na+ accumulation in acetylcholine-induced desensitization was investigated in guinea pig ileal longitudinal muscle. Desensitization was induced by the pretreatment with acetylcholine (10-4 M, 30 min)and was expressed by the rightward shift in the concentration-response curve for acetylcholine after the treatment. The same treatment with acetylcholine caused accumulation of cellular Na+ that amounted to about 3.5-fold of the control level. To study the relationship between the gain of cellular Na+ and the development of desensitization, we treated the muscle strips with acetylcholine under the condition in which the external Na+ concentration ranged from zero to 149.2 mM. The result showed that cellular Na+ content is closely related to the extent of desensitization; that is, desensitization was at the lowest level when acetylcholine induced no increase in cellular Na+, while desensitization developed in proportion to the increase in cellular Na+ content. However, when cellular Na+ was increased by another method (by the treatment with ouabain), the inhibition of the acetylcholine response was far less than that observed in the case of desensitization. We concluded that both muscarinic stimulation and the accompanying accumulation of cellular Na+ are required for desensitization to occur in full. This desensitization could be the result of a muscarinic stimulated and cellular Na+-dependent mechanism.
To determine whether insulin resistance is responsible for the development of hypertension, we examined whether blood pressure changes in an insulin-resistant animal that was given a fructose solution as their drinking water. Wistar Kyoto rats that drank a 10% fructose solution for 10 weeks showed significant increases not only in plasma triglyceride and insulin levels but also in systolic blood pressure. The decrease in blood glucose in response to the intraperitoneal injection of insulin (0.2-1.0 U/kg) was slight in these fructose-drinking rats. To confirm whether insulin resistance contributes to the observed hypertension, we examined the effect of pioglitazone, an insulin sensitizer, on blood pressure in rats given a 10% fructose solution. When pioglitazone was administered to the rats at a dose of 10 mg/kg/day for 4 weeks from 12 weeks of age, plasma triglyceride and insulin levels and systolic blood pressure decreased, and blood glucose reduction in response to insulin was normalized. These results suggest that insulin resistance is responsible for the development of hypertension in fructose-drinking rats.
Platelet-derived growth factor (PDGF)-BB induces tube formation by the differentiating (tube-forming)endothelial cells (EC)of rat thoracic aorta, although PDGF-BB does not affect the proliferative EC (increasing the cell numbers)at the progression phase. These changes in the responses to PDGF-BB were due to the phenotype-dependent expression of PDGF β-receptor (PDGFR-β)on EC because PDGFR-β-like immunoreactivity was observed in the angiogenic EC forming a tube-like structure in 35-day culture with 10% fetal bovine serum, but not in the proliferative EC in 5-day culture. To elucidate the functional role of PDGFR-β in the alteration of EC phenotype, the influence of PDGF-BB on the cell cycle of EC was investigated by flow cytometry. This analysis demonstrates that PDGF-BB blocks the transition from the G0 to G1 phase in the 35-day cultured EC, although no effect was observed on any phases of the cell cycle in 5-day culture. We conclude that 1)PDGFR-β is expressed in mature angiogenic EC of rat aorta, and 2)PDGF-BB may contribute to promotion of the EC differentiation with tubular morphogenesis by inhibiting cell growth.
Dark Agouti (DA)and Lewis rat strains were tested for susceptibility to collagen-induced arthritis (CIA)and for development of cellular and humoral immune responses to type II collagen (CII). All of the DA rats developed arthritis following a single intradermal injection of more than 20 μg of CII (130-150 μg/kg rat weight)and showed a swelling rate of more than 100% in the hind paws. The swelling rate showed little deviation among the animals. There was a strong correlation between the severity of the arthritis and the strength of the immune response to CII in DA rats with CIA. Following immunization with even 800 μg of CII (3.8-4.2 mg/kg rat weight), Lewis rats showed a maximum rate of hind paw swelling of only 45%. In the pharmacological studies, prednisolone, indomethacin, FK-506 and mizoribine all suppressed arthritis in DA rats. These findings suggest that DA rats are more susceptible to CIA than Lewis rats and that CIA in DA rats as well as in Lewis rats is serviceable as an experimental animal model of rheumatoid arthritis.
It has been reported that the immunosuppressant mizoribine (MZR)inhibits T cell proliferation by depleting intracellular guanine nucleotides via competitive inhibition of inosine 5''-monophosphate (IMP)dehydrogenase in the purine metabolism pathway. This study was performed to determine if the mechanism by which MZR suppresses the proliferation of mouse B cells and antibody production by these cells is dependent on the depletion of intracellular guanine nucleotides. Stimulation of purified splenic B cells of mice with lipopolysaccharide (LPS), a mitogen to B cells, increased both proliferation and antibody production. MZR suppressed both of these functions in a dose-dependent fashion. MZR also caused a decrease in the amount of intracellular guanosine 5''-triphosphate (GTP). When the cultures were grown on plates containing guanosine plus 8-aminoguanosine, the amount of intracellular GTP, which had been reduced by MZR, was restored. Furthermore, the repletion of GTP pools restored both proliferation and antibody production almost to their previous levels. These results suggest that MZR suppresses antibody production and proliferation of B cells by acting directly on B cells. Furthermore, it is suggested that the inhibitory effect of MZR on antibody production, as well as on T cell proliferation, is dependent on the decrease in intracellular guanine nucleotide pools of mouse B cells.
We examined the effect of 20-hydroxyecdysone (20-HE), a neurosteroid found in insects that is involved in their developmental process, on both tonic convulsion and absence-like seizure in spontaneously epileptic rat (SER). When 20-HE was given orally to SER at 25 200 mg/kg, significant decreases of the tonic convulsion were observed with 100 and 200 mg/kg. Pretreatment of the animal with bicuculline (1 mg/kg, i.p.)antagonized the inhibitory effects of 20-HE. However, absence-like seizures were not affected by 20-HE. These findings indicate that 20-HE produces antiepileptic effects on tonic convulsion by acting on the modulatory site of GABAA receptors.
Intracerebroventricularly (i.c.v.)administered nitric oxide (NO)donors, 3-morpholinosydnonimine (SIN-1)(100-500 μg/animal)and sodium nitroprusside (SNP)(100-250 μg/animal)dosedependently inhibited the rat gastric acid secretion evoked by vagal stimulation at 3 Hz. Furthermore, the inhibitory effect of SIN-1 (250 μg/animal)was more marked and its onset was more rapid than that of SNP (250 μg/animal). The SIN-1 (250 μg/animal)-induced antisecretory effect was abolished by both splanchnicotomy and phentolamine (5 mg/kg, i.m.), and also by indomethacin (500 μg/animal, i.c.v.). These results suggest that i.c.v. administered NO donors inhibit vagally evoked gastric acid secretion by activation of central sympathetic outflow. Central prostaglandin is probably implicated in this NOmediated antisecretory effect.