Cyclic Nucleotide Systems in the Microcirculation of Mammalian Brain
The cellular elements of the central microcirculation, namely the capillaries, choroid plexus and pia, contain adrenergic nerve endings whose functions may be involved in the regulation of permeability (1–6). An important aspect of noradrenergic action is stimulation of the receptor enzyme, adenylate cyclase with concomitant formation of adenosine cyclic 3′,5′-monophosphate (cyclic AMP). Recent work that I did with co-investigators (7–10) and the works of others (11–15) showed that the cellular components of the microcirculation contain active adenylate cyclase systems capable of responding to a variety of neurohumoral agonists, including norepinephrine. Joō (16) found that an infusion of dibutyryl cyclic AMP yielded an enhanced number of pinocytotic vesicles in mouse cerebral capillaries, and suggested that the cyclic nucleotide has a role in central nervous system transport mechanisms. In this chapter I will discuss our previous work and present new data characterizing the specific nature of the receptor enzymes in rat and rabbit cerebral microvessels. In addition, since the cerebral capillaries develop altered permeability in certain pathologic conditions such as hypertension (6,17–19), we will report changes seen in the cyclase system of cerebral capillaries from the spontaneously hypertensive rats (SHR).
KeywordsAdenylate Cyclase Choroid Plexus Cyclic Nucleotide Brain Capillary Pinocytotic Vesicle
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