Daily profiles of N-acetyltransferase measured at a single time in rat pineal glands, retinas, and Harderian glands.

Serotonin N-acetyltransferase activity (NAT) exhibited a daily cycle in light:dark (LD) 14:10 when it was measured in pineal glands taken from rats killed at a sequence of time points. The ratio of peak subjective night NAT to minimum subjective day NAT was 10.9/0.3 nmol per pineal gland per hour. When the rats were placed in constant dark the rhythm persisted (8.2/0.02). When the rats were placed in constant light the rhythm persisted with markedly attenuated amplitude (0.6/0.02). We also measured NAT profiles in rat pineal glands, Harderian glands, and retinas with alternative methods. We kept rats on six LD 14:10 light-dark cycles with lights-out beginning at midnight, 2 AM, 4 AM, 6 AM, 8 AM, or 10 AM and killing all the rats at one time point, 10 AM. We examined the NAT time profiles 4, 8, and 11 days following placement of the rats in the phase-shifted cycles. In addition, we measured the NAT profile in LD 2:22 and LD 22:2 by keeping the rats on twelve cycles for 11 days and killing all the rats at one time. Pineal NAT exhibited a rhythm in all the cycles: peak-dark/nadir-light values (nmol product per gland per hour) were 15.6/0.1 in LD 14:10, controls killed at successive time points. The ratios for the profiles obtained using the one time point procedure were 16.7/0.1 in LD 14:10 8.5/0.2 in LD 22.2, and 12.9/0.2 in LD 2.22. Increasing the photoperiod reduced the time to the NAT peak.(ABSTRACT TRUNCATED AT 250 WORDS)