Reactivity to bradykinin and potassium of the isolated duodenum from rats with genetic and renal hypertension

Abstract

1 The biphasic (relaxation-contraction) response of the isolated duodenum was used to study the reactivity of non-vascular smooth muscles in genetic (SHR) and renal hypertensive rats compared to their respective controls (WKY and Wistar). 2 For the contractile component of the response to bradykinin, the duodenum from WKY rats was more sensitive, whereas the duodenum from SHR was both more sensitive and hyperreactive, compared to that from Wistar rats. 3 The relaxant component of the response to bradykinin was present in the duodenum of both WKY rats and SHR, but was concentration-dependent only in the WKY group. 4 The relaxant response to K+ was very small in SHR, and was not concentration-dependent. 5 The concentration-response curves for relaxant responses to adrenaline and for contractile responses to acetylcholine did not differ in the SHR and WKY groups. 6 Ca2+/Mg2+-ATPase activity was found to be markedly reduced in the SHR group. 7 No qualitative or quantitative differences were observed between the responses of the duodenum of renal hypertensive rats and those of their normotensive controls. 8 It is proposed that the altered reactivity of the SHR duodenum is due to changes in ion handling by the smooth muscle cell membrane.

Corticosteroid modulation of Na +‐K+ pump‐mediated relaxation in maturing airway smooth muscle

“…We have also noted no difference in the KCl-induced relaxation in TSM pretreated with the calciumchannel blocker, nifedipine (Schramm & Grunstein 1989). Thus, while the potential contribution from other transmitters or ion transport mechanisms cannot be completely ruled out, our findings are comparable to those previously reported using the same method to assay maximal physiological Na+-K+ pump activity in vascular (Feletou & Corticosteroid effects on the airway Na+-K+ pump T et Rinaldi & Bohr, 1989: Shubat et al, 1990, gastrointestinal (Miasiro et al, 1985;Muller et al, 1989), and airway smooth muscle Gunst & Stropp, 1988;Schramm & Grunstein, 1989: Schramm & Grunstein, 1995.…”

Effect of treatment with vitamin D3 on the responses of the duodenum of spontaneously hypertensive rats to bradykinin and to potassium

“…The relaxation induced by the increase of extracellular potassium is attributed to hyperpolarization due to the stimulation of the Na+/K' pump (Rinaldi et al, 1989). The decreased relaxant response of the SHR and WKY duodenum to potassium confirmed previous findings from our laboratory which showed an inhibition of the Na+/K' pump in this strain (Miasiro et al, 1985). Our results therefore suggest that the normalization of the relaxant response of the SHR by chronic treatment with vitamin D3 may be due to an activation of this pump by vitamin D. The normalization of the Na+/K' pump activity could also contribute to the hypotensive effect of vitamin D3, since Bukosi et al (1986) has already suggested a link between Na+/K' pump activity normalization and the hypotensive effect of dietary calcium.…”

“…At bradykinin concentrations of 4 nm and above, the SHR duodenum responded with a concentration-dependent contraction preceded by a small relaxation. This predominantly contractile response of the SHR duodenum contrasted with the predominantly relaxant response of the NWR and WKY duodenum, in agreement with a previous report (Miasiro et al, 1985 The SHR which received 2% calcium lactate in the drinking water, or a daily diet supplementation with 12.5 jig vitamin D3, had their blood pressure reduced to normal levels, whereas no significant changes were observed in the blood pressure of WKY animals submitted to the same treatment (Figure 2). …”

“…The ED50 values for the relaxant component of the responses of both NWR and WKY rats were significantly decreased after the treatment (Table 1) Duodenum preparations from SHR and WKY presented an impaired relaxant response to K+ that was interpreted as a result of the inhibition of the Na+/K+ pump activity in these animal strains, as compared with the NWR (Miasiro et al, 1985). After vitamin D3 treatment, duodenum from all three strains presented a significant increase of the relaxant response to K+ (Figure 3).…”

“…In normal rats, the response to low concentrations of this agonist consists only of a relaxation, whereas higher concentrations elicit relaxation followed by contraction (Boschcov et al, 1984). Previous work from this laboratory showed that the response of the SHR to bradykinin is predominantly contractile, with suppression of its relaxant component (Miasiro et al, 1985). We The rat duodenum preparation was set up as previously described (Boschcov et al, 1984).…”