Adrenergic control of intrarenal arteries of rabbits

A comparative study of the adrenergic control of two sequential rabbit intrarenal arteries of differing diameter [intrarenal branch artery (IRBA) - unstretched lumen diameter (ULD) ~300 μm and interlobar artery (ILA) - ULD ~250 μm] has been conducted. The neurogenic contractile response of isolated segments in relation to the maximum response to l-norepinephrine (NE) was minimal (8 Hz response ~30% of maximum contraction) and similar in both types of arteries. Phentolamine (PTA) (10-6 M) blocked neurally evoked contractions of the IRBAs at 2, 4, and 8 Hz and of the ILAs at 2 and 4 Hz. (8 Hz responses were not entirely blocked in 3 out of 8 ILAs). The sensitivity to exogenous NE decreased with a decrease in intrarenal vessel diameter, whereas the maximum active smooth muscle cell stress to NE was \u3e3 x 105 N/m2 for each vessel. All arterial segments constricted in response to histamine (H) and NE with equal maximal effects; however, sensitivity to H was greater in the smaller artery (ILA). The comparative contractile responses to nerve stimulation and exogenous NE in sequential renal arteries contrasts to the pattern of these responses in sequential arteries in any other rabbit regional bed previously studied (pulmonary and ear vasculature)