The causal link between nutritive resources and fertility is well established (reviewed in ), and considering (in the female) the enormous metabolic requirements of pregnancy and lactation, it seems to be part of an effective strategy to ensure that energy resources are not wasted on reproductive efforts that are unlikely to succeed. However, while the HPG axis can be rapidly modulated by glucopri-vation, this may not be the only metabolic signal to which the reproductive axis responds. ventolin 100 mcg
Indeed, it is also well established that an animal’s reserves of adipose tissue can influence reproductive capability in two ways: 1) the timing of the onset of puberty (specifically the time of first ovulation in females) and 2) the ability to maintain reproductive function during adulthood. Schneider and Wade have demonstrated that fasting-induced anestrus occurs more rapidly in lean hamsters than in fat hamsters. Rats maintained on a high-fat diet come into first estrus earlier than do animals fed on a low-fat diet, yet body composition is similar among animals upon reaching first estrus. Similarly, adolescent girls often differ in height and weight at menarche, but tend to have a similar percentage of body fat. The observation that women with a low percentage of body fat are often amenorrheic led Frisch and McArthur to propose that minimal body fat levels are required for both the onset and maintenance of menstrual cycles in women. One of the criticisms of the ‘‘critical body fat’’ hypothesis has been the limited number of viable candidates for a molecule whose function is to convey body fat levels to the brain, in which it could in turn affect hypothalamic output.