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Some biochemical studies on the pituitary gonadotrophin(s) of the ricefield eel, Monopterus albus (Zuiew)

by Ng, Tzi-bun

Abstract (Summary)
(Uncorrected OCR) i

Abstract of thesis entitled "Some biochemical studies on the

pituitary gonadotrophin(s) of the ricefield eel, Monopterus albus (Zuiew)"

Submitted by NG TZI BUN

for the degree of Master of Philosophy

at the University of Hong Kong in July, 1976

Two types of gonadotrophic activities have been

identified in the pituitary of Monopterus albus with the aid of specific bioassays employilg the rat as the recipient, but

the Monopterus pituitary homogenate is completely devoid of

potency when tested in the mouse. Assays of pituitaries of

M. alb~ at various sexual phases reveal a marked increase

in the FSH/LH ratio when the fish undergoes sex reversal.

The highest amount of LH-like activity contained in the female

Monopterus pituitary indicates a possible preovulatory surge

of LH which triggers off the proliferation of interstitial

Leydig cells and the development of testicular lobules

characteristic of sex reversal in M. albus.

The Monopterus pituitary homogenate is capable of

depleting the ovarian cholesterol content of immature

pseudopregnant rats, and elevating the coagulating gland

fructose level, ventral prostatic citric acid content and

alkaline phosphatase activity in the prepubertal mal~;.rat.

These findings yield corroborative evidences of a LH-like

hormone in Monopterus pituitary. The Monopterus pituitary homogenate is also active in stimulating the uptake of 32p by the testes and ovaries of day-old chick.

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Administration of Monopter~~ pituitary homogenate into prepubertal male rats ensues in a rise in the activities

of enzymes known to be related with steroid biosynthesis,

e.g. isocitrate and alcohol dehydrogenases. Enzyme activities

in the luteinized ovaries of prepubertal rats are, however,

unaffected after similar treatments, even when asoorbio acid

and cholesterol have been depleted to a large extent, inferring

that the effects on enzymes activities and ascorbic acid and

cholesterol oontents may represent two facets of hormonal

actions that may not bear a simple direct relationship to

one another.

Glycolysis can be stimulated in the luteinized rat

ovary by an ~ !!!2 administration of Monopterus pituitary homogenate, and in the prepubertal rat ovary after a brief

exposure to Monopterus pituitary homogenate ~ vitro,

followed by incubation ~ vitro. Thus the Monopterus

pituitary is seen to contain a hormone, or hormones, capable

of stimulating the entry of glucose into, and subsequent

metabolism in, ovarian follicles before antrum formation,

as well as in corpora lutea. The persistent hormonal effect

observed after washing in a hormone-free medium provides an

evidence of the binding affinity of rat ovarian receptors to

the hormone(s) in Monopterus pituitary homogenate.

The FSH-like activity appears to be a conformational1y

more stable entity to which the presence of sialic acid is

requisite for the expression of its biological effect. In contrast, the LH-like activity does not depend on sialic acid for its biological activity, and is easily abolished by reagents which disrupt molecular conformations. Both activities

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are retained after treatment with exopeptidases and endopeptidases, but are lost after chemical modification of the histidine,

tyrosine and tryptophan residues in which the active cores of

the hormones may lie.

The marked ohange in the pituitary FSH/LH ratio accompanying sex reversal, the manifestation of activity of aotivity of Monopterus pituitary homogenate in assays specific for FSH and LH, and its differential stability to chemicals and enzymes in the assays, furnish indirect evidences of the existence of two types of gonadotrophins in the Monopterus pituitary, although a final conclusive proof can reside only in the physicochemical purification and characterization of the hormones, and designation of distinct biologioal actions to each of them.

Bibliographical Information:

Advisor:

School:The University of Hong Kong

School Location:China - Hong Kong SAR

Source Type:Master's Thesis

Keywords:eels monopterus albus gonadotropin

ISBN:

Date of Publication:01/01/1976

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