Control of Reproduction in Mammals 
of drugs will inhibit the production of ovulatory neurohumour 
by the hypothalamus. These drugs include barbiturates, cer- 
tain tranquillizers, morphine and ether. ‘The doses necessary 
for such inhibition appear to be rather high and this is probably 
why their experimental study in the human has not been carried 
on to any extent. The situation is quite different with proges- 
terone, where we can clearly see ovulation inhibition at physio- 
logical doses. 
Experimental work with loci other than the hypothalamus 
has been much more limited. Thus no substances have been 
found which have a direct stimulating or inhibiting effect on 
the pituitary, i.e. which do not act via the hypothalamus. 
Several means of affecting LH in the circulating blood have 
been investigated. These include extracts from plants (Litho- 
spermum ruderale and Lycopus virginicus) and from pituitary glands, 
foetal blood serum and human urine. None of these agents are 
chemically defined, and the nature of their action is often 
dubious: the plant extracts are postulated as acting by destroy- 
ing gonadotropin by enzyme action, and the animal substances 
as acting as competitive inhibitors to gonadotropin. Perhaps 
the most promising inactivator at present is LH antibody, which 
is prepared by making an antiserum to LH. It inactivates LH 
in the blood by combining with it to produce an inactive com- 
pound. The fact that the LH antibodies of some animal species 
are able to inactivate the LH of other species implies that it 
might be possible to use animal antibodies in man; however, 
very much remains to be learned about long-range effects, the 
possibility of isoimmunity, sensitivity reactions and so on. 
Concerning the fourth locus—the ovarian follicle itself—again 
there is only limited experimental work to consider. Curiously, 
the most effective drug which directly inhibits follicle rupture 
is reserpine, a substance which also inhibits the hypothalamus. 
Certain steroids (i.e. substances with the same chemical skeleton 
as the sex hormones) are active also, but again at very high 
doses. It should be emphasized, however, that animal work in 
this area is still at an early stage and it may be predicted that 
interesting discoveries will come in the future. 
SI 
