Microvascular response to blockade of prostaglandin synthesis in rat skeletal muscle

The contribution of endogenous prostaglandins (PGs) to the control of arteriolar diameter in the microcirculation is incompletely defied and has only been studied in drug-anesthetized animals. To test the possibility that endogenous PGs are tonically released to exert a net dilator influence at certain levels in the microcirculation, television microscopy was used to quantitate the arteriolar responses in the rat cremaster muscle to local blockade of PG synthesis with indomethacin. Rats were decerebrated by a midcollicular transection and were allowed to recover from surgical anesthesia. The cremaster muscle with intact circulation and innervation was suspended by sutures in a temperature-controlled Krebs bath. Diameters, vasomotion frequency, and vasomotion amplitude of arterioles at several anatomic levels were measured before and after local inhibition of PG synthesis in the presence and absence of alpha-adrenergic receptor blockade. Inhibition of PG synthesis produced marked constriction (42-66% of control) at all arteriolar levels, with greater responses occurring in the smaller arterioles. PG synthesis blockade increased vasomotion frequency in arterioles that exhibited spontaneous vasomotion during control periods, and blockade induced vasomotion in vessels lacking spontaneous vasomotion. Pretreatment with phentolamine significantly attenuated the constriction and augmentation of vasomotion. These data indicate that dilator PGs participate in the moment-to-moment regulation of arteriolar tone and local blood flow in skeletal muscle. Further, their mechanism of action may involve alterations in neuronal norepinephrine release or alpha-receptor sensitivity.