Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. II

cervical mucus when the corpus luteum regressed, even though the
cattle were still receiving the oral progestagen, and (b) the
ovaries were larger than normal, due to excessive follicular fluid,
indicative of FSH activity. Increasing the dose, within fairly
narrow limits, had little effect. They concluded that MGA did not
simulate the corpus luteum and that it suppressed LH more effec-
tively than FSH. Zimbelman (1966), in summarising the activities
of MGA, concluded that it did not effectively suppress release of
FSH but caused an increase in the level of pituitary LH consistent
with an inhibition of release, and that this was consistent with the
hypothesis concerning two centres for the release of LH.

The whole question of the qualitative effects of different pro-
gestagens is wide open. It is a difficult field because it is
confounded by quantitative effects, different durations of activity
and possibly by species differences.

TABLE 7
Methods of evaluation of endocrine status

1. Direct assays of hormone content

a. Pituitaries and ovaries
b. Effluent blood

c. Peripheral blood

d. Target tissues

2. 1Indirect estimates of hormone action

a. Morphology, histology and histochemistry
i. Pituitary and ovaries
ii. Reproductive tract
b. Enzymology and biochemistry of the tract
c. Characteristics of cervical mucus
d. Overt oestrus =- incidence, duration,
intensity
e. Spermatozoa - transport and survival in
female tract

3. Methods for the evaluation of endocrine status
The endocrine status of an animal at any one time can be

assessed directly by assays of hormones, or indirectly by the end
points of their action (Table 7).

1365

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