PHYSIOLOGY OF ANTERIOR HYPOPHYSIS 



249 



tomized animals of any strain can be used 

 for the assay of purified ICSH, but only 

 those of the Long-Evans strain are suitable 

 of the assay of impure preparations. Loraine 

 and Diczfalusy (1958) concluded that the 

 response of the ventral prostate of the hy- 

 pophysectomized immature male rat to hu- 

 man menopausal gonadotrophin and HCG 

 is not affected by the simultaneous admini- 

 stration of prolactin. Most important, per- 

 haps, is the fact that FSH does not affect 

 the prostatic assay for LH (Greep, van 

 Dyke and Chow, 1941 ; Lostroh, Squire and 

 Li^, 1958 j. 



According to Lostroh, Squire and Li 

 (1958) , "the hypophysectomized male rat of 

 the Long-Evans strain has been a satisfac- 

 tory animal for assaying preparations of 

 ICSH when the weight of the ventral pros- 

 tate is used as a measure of the activity 

 and the response is represented as a loga- 

 rithmic function of the dose. . . . The sensi- 

 tivity of the assay is such that a total dose 

 level of from 0.010 to 0.060 mg. is sufficient 

 for assay purposes when the subcutaneous 

 route is employed." 



The Weaver finch test for LH, developed 

 by Witschi (1940, 1955), is gaining accept- 

 ance as a valuable means of identifying 

 this gonadotrophin (Segal, 1957). The test 

 is carried out on African finches of the 

 genera Euplectes and Steganura. Regenerat- 

 ing white feathers of the ventral pterylae 

 in females or in males in eclipse plumage 

 react to a single injection of LH by the 

 formation of a black bar formed as a result 

 of melanm-dep6sition. The test is held to 

 be specific for pituitary LH, but the evi- 

 dence for this view is not yet conclusive. 

 The reaction is independent of the sex 

 glands. The observation that the Weaver 

 finch test does not detect LH in menopausal 

 urine (Witschi, 1955) as does the ventral 

 prostate method (Greep and Chester Jones, 

 1950b; Loraine and Diczfalusy, 1958) needs 

 further exploration. 



Evidence submitted within the past year 

 (Parlow, 1958) suggests that LH produces 

 a fall in ascorbic acid content of the ovaries 

 of pseudopregnant rats and promises to form 

 the basis of a further and much more sensi- 

 tive means of assaying the luteinizing hor- 

 mone. 



C. LUTEOTROPHIN (PROLACTIN) 



1. Chemical Features 



Prolactin has been isolated in a form 

 satisfying all the available physicochemical 

 criteria of protein homogeneity and ex- 

 hibiting no biologic activity other than that 

 believed to be attributable to the hormone 

 (for latest evidence see Li, 1957). Prolactin 

 was the first in this category of protein 

 hormones to be obtained in crystalline form 

 (White, Catchpole and Long, 1937; White, 

 1943) — a notable achievement even though 

 crystallization is no necessary indication 

 of purity. Prolactin has mainly been ob- 

 tained from the hypophyses of beef and 

 sheep and although there may be minor spe- 

 cies differences in the composition of the 

 hormone as indicated by a slight difference 

 in solubility, the preparations otherwise be- 

 have identically. They have an isoelectric 

 point of 5.7 and a molecular weight of about 

 3200 (White. 1949). 



2. Physiology of Luteotrophic Hormone 



[Prolactin ) 



Riddle, Bates and Dykshorn (1932) pro- 

 posed the term prolactin to describe a pitui- 

 tary activity which stimulated the crop sac 

 of pigeons. In mammals prolactin was shown 

 to possess also lactogenic and luteotrophic 

 activity. It has not been unequivocally dem- 

 onstrated that prolactin, lactogenic hor- 

 mone, and luteotrophin are identical nor 

 that luteotrophic manifestations are essen- 

 tial for luteal function except in the rat. 

 For the purposes of this chapter, however, 

 it is regarded as semantically legitimate to 

 discuss LTH as a gonadotrophin, although 

 scientifically neither its activity nor its 

 identity with prolactin has been rigorously 

 proved. 



As noted, the rat is the only animal in 

 which a luteotrophic action of prolactin has 

 been conclusively demonstrated (Astwood, 

 1941 ; Cutuly, 1941 ; Evans, Simpson and 

 Lyons, 1941 ; Evans, Simpson, Lyons and 

 Turpeinen, 1941 ) . Confirmatory observa- 

 tions have been reported by Lyons (1942), 

 Tobin (1942), Fluhmann and Laqueur 

 (1943), Everett (1944), Sydnor (1945). 

 Greep and Chester Jones (1950a). Tests of 

 the luteotrophic action of prolactin in other 



