Responses to BRL 37344 in the presence of phentolamine (1puM) and propranolol (1 pM) were antagonized by (±)-cyanopindolol (IpM), with an apparent pA2 value of 6.67. Responses to isoprenaline, under the same conditions, were antagonized in a competitive manner by (±)-cyanopindolol (0.1 to 10pM), with the slope of the Schild plot close to unity and a pA2 value of 7.12. 6 The resistance of the relaxant responses to antagonism by phentolamine and propranolol, along with the relatively high potency of the #3-adrenoceptor agonist BRL 37344 and the antagonism of 'resistant' responses by (±)-cyanopindolol would suggest that 'atypical' f6-adrenoceptors, similar to the fl3-adrenoceptors of rat adipocytes and other tissues, exist in the rat distal colon.

No abstract

To evaluate the local circulatory changes that accompany chronic localized work, we studied the effects of a 4-wk handgrip work protocol on maximal forearm work-related blood flow (ml X min-1 X 100 ml-1) in the nondominant forearms of six normal subjects. The reactive hyperemic blood flow response (RHBF) was also evaluated pre- and posttraining in both forearms of each subject to determine whether maximal vasodilatory capacity would be enhanced. In addition, maximal O2 consumption (VO2max) was measured. We found that chronic handgrip work led to an increase in work-related blood flow (before, 22.4; after, 32.1; P less than 0.05); a drop in work-related minimal resistance (R) (before, 6.4; after, 4.1; P less than 0.05). RHBF rose in the chronically exercised extremity by 30% (before, 33.5; after, 43.7; P less than 0.05) as minimal R fell (before, 3.2; after, 2.2; P less than 0.05). RHBF and R in the unstimulated dominant forearm remained unchanged (blood flow: before, 33.5; after, 31.0; NS; R before, 3.2; after, 3.2; NS). VO2max (ml X kg-1 X min-1) did not change (before, 35.7; after, 34.0). These findings show that localized skeletal muscle forearm work is associated with a localized increase in vasodilation (RHBF). Thus the vascular system appears to be an independent integral partner in the training process.

No abstract

1 Experiments were carried out in order to characterize the receptors mediating relaxant responses to catecholamines in the rat gastric fundus. The effects of noradrenaline, isoprenaline and the 'atypical' or 13-adrenoceptor agonist, BRL 37344, on methacholine-induced tone were measured. Prazosin, propranolol and cyanopindolol were used as antagonists. 2 Relaxant responses to noradrenaline, in the presence of propranolol (1 M) were antagonized in a concentration-dependent manner by prazosin (0.01 to 1,pM), although this antagonism was weak and non-competitive in nature. Relaxant responses to isoprenaline, in the presence of prazosin (0.1 ,UM), were antagonized only by the highest concentration of propranolol (1 pM) giving a pKB of 6.3. BRL 37344 also relaxed the rat gastric fundus in the presence of prazosin (0.1 pM), and the responses to BRL 37344 were unaffected by propranolol (1 pM). 3 Tachyphylaxis to BRL 37344 was observed, a second concentration-response curve being significantly shifted to the right. Exposure of tissues to BRL 37344 (1 pM) between concentration-response curves also caused an 11 fold rightward shift in the response to isoprenaline. 4 In the presence of prazosin (0.1 uM) and propranolol (1,UM), the rank order of potency of the agonists was: (-)-isoprenaline (1.0) > (-)-noradrenaline (0.39) > BRL 37344 (0.10). 5 Responses to BRL 37344 in the presence of prazosin (0.1 pM) and propranolol (1 pM) were antagonized by (±)-cyanopindolol (1pM), with a pKB of 6.56. Responses to isoprenaline, under the same conditions, were antagonized in a competitive manner by (±)-cyanopindolol (0.1-1 uM), with the slope of a Schild plot close to unity and a pA2 value of 7.44. 6 The resistance to blockade by prazosin and propranolol and the antagonism by cyanopindolol of the responses mediated by isoprenaline and BRL 37344 suggest that atypical f-adrenoceptors similar to 'atypical',f-adrenoceptors in rat adipocytes and other tissues are present in the rat gastric fundus.