LOCAL AND SYSTEMIC ALTERATIONS IN CYCLIC-3',5'-AMP PHOSPHODIESTERASE ACTIVITY IN RELATION TO TAIL REGENERATION UNDER HYPOTHYROIDISM AND T-4REPLACEMENT IN THE LIZARD, MABUYA-CARINATA

To establish the relationship between thyroid hormone and cyclic Adeno sine monophosphate (cAMP) during lacertilian tail regeneration, cAMP p hosphodiesterase, the hydrolytic enzyme of cAMP, was assayed in the ta il regenerate, liver, and skeletal muscle of control (group A), chemic ally thyroidectomized (group B), and thyroidectomized and T-4-replaced (group C) animals during various periods of tail regeneration. Enzyme activity was elevated in all three tissues of group B animals. Animal s of group C showed an intermediate level of enzyme activity between c ontrols (group A) and experimental animals (group B). These observatio ns suggest a possible regulatory role of thyroxine in maintaining opti mum levels of phosphodiesterase. The retardation in regeneration obser vable in the hypothyroid group of animals may be correlated with low l evels of tissue cAMP. However, the operation of other influencing fact ors on phosphodiesterase during regeneration can be surmised from the observed tendency to exhibit similar patterns of phase-specific modula tions in enzyme activity. Our observations are discussed in terms of p hase-specific involvement of cAMP in regeneration, as well as its role in other metabolic aspects and the possible mode of indirect control exerted by thyroxine on lacertilian tail regeneration. (C) 1996 Wiiey- Liss, Inc.