G. Alan Robison

Cyclic Adenosine Monophosphate in Brain Areas: Microwave Irradiation as a Means of Tissue Fixation

Amounts of cyclic adenosine monophosphate in discrete regions of the brain were estimated after exposure of rats to microwave irradiation. Amounts were highest in the cerebellum and brainstem, intermediate in the hypothalamus and midbrain, and lowest in the hippocampus and cortex. Decapitation increased the concentration of cyclic adenosine monophosphate in all brain areas, although the increase in the cerebellum was three to four times greater than that in other areas. Microwave irradiation may provide a means of rapidly fixing brain tissue in situ while permitting easy dissection of the brain. In this way artifacts produced by decapitation can be eliminated, and concentrations of heat-stable compounds in the brain can be estimated under conditions which more closely approximate those in vivo.

ADRENERGIC RECEPTORS AND CYCLIC AMP IN THE REGULATION OF HUMAN ADIPOSE TISSUE LIPOLYSIS

For the past several years our major objective has been the elucidation of mechanisms controlling the release of stored triglyceride by adipose tissue. Since derangement of such mechanisms could well be involved in important human diseases. it was felt that human adipose tissue should be studiedalong with that of appropriate experimental animals-to avoid being misled by species variation. In retrospect, this was a prudent decision since substantial differences between human and rat adipose tissue have been Rat tissue responds to a wide range of lipolytic substances including ACTH, TSH, growth hormone plus dexamethasone, glucagon, and catecholamines. Human adipose tissue is much more selective, responding to catecholamines, TSH, and crude human pituitary fractions associated with TSH, but not responding to ACTH (see FIGURE 1 ) , glucagon, or growth hormone plus dexamethasone. In view of such observations, we felt it important to determine if cyclic AMP played a central role in human adipose tissue lipolysis as it appears to do in the rat. For this purpose, the effects of cyclic AMP, its dibutyryl derivative (DAMP), and theophylline, singly and in combination with insulin, on lipolysis by human and rat adipose tissue have been observed. We have also evaluated the hypothesis that adrenergic receptors may be linked to the cyclic AMP system.x. According to this hypothesis, interaction of a catecholamine with beta receptors causes activation of adenyl cyclase and an increase in cyclic AMP, whereas interaction with alpha receptors reduces the effective concentration of cyclic AMP and leads to an opposite effect on cell function. To evaluate this hypothesis, we have observed the effects of propranolol, a beta blocking agent, and phentolamine, an alpha blocker, on basal and stimulated lipolysis of human and rat cells and tissue fragments. The stimulating substances used were isoproterenol, a relatively pure beta agonist, and epinephrine, a mixed agonist having both alpha and beta stimulating capabilities.