Pituitary response to LRH and TRH stimulation and peripheral steroid hormones in conscious and anaesthetized adult male rhesus monkeys (Macaca mulatta)

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Abstract
Adult male rhesus monkeys are aggressive animals and very difficult to handle. Hence experimental manipulations necessarily involve the use of restraint procedures, either chemical or physical, which may influence endocrine functions. Therefore, the effects of ketamine anesthesia on basal hormone levels and on the pituitary response to LRH [luteinizing hormone releasing hormone luliberin] and TRH [thyrotropin releasing hormone, thyroliberin] were investigated in 4 adult male rhesus monkeys. Values were compared to those obtained from the same animals restrained in primate chairs for approximately 48 h, a procedure to which they had become accustomed over the preceding 6 mo. Serum cortisol levels under anesthesia were at all times lower than in conscious monkeys but increased after 2 h to values twice as high as measured initially. Serum testosterone concentrations were not significantly different on the 2 occasions, but levels under anesthesia were slightly higher initially than in the conscious monkeys and decreased gradually over the 3 h test period. Initial prolactin levels were lower in the anesthetized monkeys and increased 2-3-fold after 90 min; values at 3 h were not significantly different from those in conscious monkeys. TRH [i.v.] elicited a similar response in prolactin on both occasions, maximum values occurring after 15-30 min and returning to basal levels after 3 h. The maximum values attained and the area under the response curves were higher under anesthesia. LRH stimulation resulted in a 15- and 30-fold increase in serum levels of biologically active LH [lutropin], with and without anesthesia, respectively. Basal levels were not significantly different on the 2 occasions. The area under the LH response curve was higher in 3 of the 4 monkeys without anesthesia. The extent to which results in conscious monkeys are affected by stress is difficult to assess. Since neither handling technique allows for the collection of true basal data, it is paramount to standardize and define the conditions under which experiments, and even routine blood sampling, are performed in male rhesus monkeys.