Effects of adenosine and guanosine cyclic phosphates and their corresponding nucleotides and nucleosides on vitamin A-induced epidermal tumor promotion and growth in hamster cheek pouch.

Adenosine and guanosine cyclic monophosphates (cAMP and cGMP) exerted opposite effects at similar concentration and similar effects at markedly different concentrations on the yields of tumors promoted by vitamin A in hamster cheek pouch. Increasing the concentration of cAMP between 10(-5) M and 10(-3) M was associated with increases in tumor yield and diameter which partially or completely overcame the net tumor promotion inhibitory effects which were sometimes seen at 10(-5) M cAMP. In contrast, increasing the concentration of cGMP between 10(-5) M and 10(-3) M caused the net effects to change from increases to decreases in tumor yield without much change in diameter. The relative magnitudes of the tumor yield increasing and decreasing effects of the cyclic nucleotides varied substantially between experiments at constant concentration of cyclic nucleotide. Adenosine-5'-monophosphate (AMP) showed simultaneous tumor promotion inhibitory and growth stimulatory effects, the former effect being similar to that of cAMP but tumor yield decreased rather than increased as concentration of AMP was increased whereas the opposite occured with cAMP. Guanosine-5'-monophosphate (GMP) showed the tumor yield increasing effect of low concentraitons of cGMP but not the yield decreasing effect of high concentrations of cGMP. Adenosine (10(-3) M) showed a significant tumor yield increasing effect similar to that of 10(-3) M cAMP. Guanosine showed no significant effects at either 10(-3) M or 10(-5) M concentrations.