Effects of short‐ and long‐term sympathectomy on vasoconstrictor responses of the rat mesenteric arterial bed

Abstract

1 The effects of short-and long-term sympathectomy were evaluated on vasoconstrictor function of constantly perfused mesenteric arterial beds isolated from rats: the effects of short-term sympathectomy were assessed at 3 and 8 days after 6-hydroxydopamine (6-OHDA) treatment of adult rats; the effects of long-term sympathectomy were assessed in adult rats treated at youth with guanethidine. 2 The relative degree of residual sympathetic innervation of the mesenteric arterial preparations was assessed by responses to electrical field stimulation (EFS; 16 Hz, 1 ms, 90 V, 30 s). Control responses were 95.6 + 3.9 mmHg (n = 35). Responses after sympathectomy were: 3 days after 6-OHDA, 2.9+0.9 mmHg (n= 15) <8 days after 6-OHDA, 14.1+2.1 mmHg (n= 14) <guanethidine, 21.1 +4.1 mmHg (n= 16).3 Three days after 6-OHDA treatment there was an increase in the sensitivities of response to vasopressin and endothelin, producing leftward shifts of the dose-response curves of 0.66+0.11 and 0.88 + 0.13 log units respectively (n = 7-11), and a small increase in sensitivity of responses to noradrenaline (NA) and ATP. The maximal response to 5-hydroxytryptamine (5-HT) was increased. In contrast, there was a decrease in maximal constriction to NA and to the ax-adrenoceptor agonist methoxamine. The a2-adrenoceptor agonist clonidine did not elicit vasoconstriction at basal tone. There was no difference in vasodilator responses to the f,-adrenoceptor agonist isoprenaline in preparations with tone raised with prostaglandin F2C, (PGF2,; 0.1 -0.3 gM).4 Eight days after 6-OHDA sympathectomy there was no significant difference in sensitivities or maximal responses to ATP, vasopressin and endothelin, but a small increase in the sensitivity of responses to 5-HT. Maximal responses to NA and methoxamine were significantly lower than the controls, but sensitivities were similar. There was no significant difference in vasodilator responses to isoprenaline in PGF2,,-raised tone preparations.5 After long-term guanethidine sympathectomy maximal responses to 5-HT and NA were significantly reduced. Responses to ATP, vasopressin and endothelin were unchanged.6 In mesenteric arterial preparations from untreated rats, ouabain (0.1 mM), a blocker of the Na+/K+ pump, significantly augmented the sensitivity and maximal responses to EFS, NA, methoxamine and 5-HT. Responses to ATP, vasopressin and endothelin were unaffected. 7 It is concluded that in the rat mesenteric arterial bed, short-term sympathectomy, where only 3% of the sympathetic nerve-mediated response remained, results in non-uniform changes in sensitivity and maximal responses to different vasoconstrictors, which cannot be entirely explained by changes in the Na+/K+ pump. Most of these changes disappeared at 8 days after 6-OHDA treatment, when nervemediated responses had partially returned. After long-term guanethidine sympathectomy, there was little change in responses to vasoconstrictors, and nerve-mediated responses were reduced to 22%. Although the variable factors are complex, it appears that in ...

Influence of neonatal sympathectomy on proximal renal resistance artery function in spontaneously hypertensive rats

“…This is in agreement with data from perfused mesenteric arterial bed preparations of guanethidine-sympathectomized Sprague-Dawley rats [17], while 6-OHDA-treated WKY show increased constrictor responses to AVP compared with control WKY [19]. The reasons for this discrepancy may be related to differences in the drugs used to produce neonatal sympathectomy or to the different rat strains and vessel types investigated.…”

“…Perfused mesenteric arterial bed preparations from SHR and WKY with guanethidineinduced neonatal sympathectomy also show supersensitivity to NE but a reduction in maximum pressure development in response to NE [11]. The latter effect of sympathectomy has also been found in guanethidinetreated Sprague-Dawley rats [17]. The differences in maximal effects of NE may result from different experimental conditions such as flow versus no flow.…”

Catecholamine sensitivity in the rat femoral artery after microvascular anastomosis

“…The duration of response after sympathectomy may be transient; after 6-OHDA sympathectomy, the changes disappeared by 8 days, 16 and this is attributed to sympathetic reinnervation. Near-complete sympathectomy is required for changes in responses to vasoconstrictor agents.…”

Lack of effect of a selective vasopressin V1A receptor antagonist, SR 49,059, on potentiation by vasopressin of adrenoceptor‐mediated pressor responses in the rat mesenteric arterial bed

“…For periarterial stimulation of sympathetic nerves bipolar ring‐type electrodes made from platinum were put around the mesenteric artery close to its aortal origin. The tissues were stimulated with supramaximal voltage (50 V) and rectangular pulses of 1 ms at a frequency of 16 Hzfor15 s(McGregor, 1965; Kawasaki et al , 1990; Ralevic & Burnstock, 1996).…”