BODY TtMPtRATURH AND FOOD AND WATtR INTAKE 



365 



therefore be assumed that the " heat loss centre " even at a normal body 

 temperature exerts a certain inhibitory tone on the release of thyrotrophic 

 hormone (T.S.H.) from the hypophysis. The strength of this inhibitory 

 tone seems to increase in relation to the rise of the temperature of the " heat 

 loss centre ", i.e. in relation to the degree of activation of central " warm 

 detectors ". 



Fig. 3. Tentative scheme depicting interaction of peripheral and central 

 mechanisms in thermoregulation. Central " warm detectors " in the Heat Loss 

 Centre apparently act as a brake on the shivering mechanism, as well as to 

 mobilize various heat loss activities (vaso-dilatation, panting, sweating). Only 

 when there is a simultaneous drive on the shivering mechanism Trom peripheral 

 cold receptors or from other factors (emotional excitation, sympathetico-adrenal 

 activation, pyrogens, etc.) does inactivation of these central " warm detectors " 

 by cooling elicit shivering. Note also that the Heat Loss Centre seems to exert 

 a tonic inhibition of thyroid activity via the hypothalamic-pituitary axis. 



There is reason to believe that other humoral mechanisms of importance 

 in the cold defence are also inhibited in a similar manner by the " heat loss 

 centre" (Andersson, Gale and Sundsten, 1962b). in preliminary experi- 

 ments the temperature of the rostral hypothalamus has been raised 1 to 2'C 

 and maintained at this level when the goats are placed in a cold environ- 

 ment. Due to the mobilization of heat loss mechanisms and to the inhibi- 

 tion of shivering and other cold defence mechanisms, the core temperature 

 of the animals falls relatively rapidly below 30'C. The hyperglycemia which 

 otherwise is seen to develop at this low body temperature does not appear 

 as long as the " heat loss centre '' is kept active by local warming. But as 

 soon as anterior hypothalamic warming is stopped, hyperglycemia rapidly 



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