ABSTRACT
The ease and rapidity with which the whole pituitary or part of the gland can be removed in Xenopus laevis, the low post-operative mortality and the fact that the animals survive the operation for more than two years, suggested an investigation into the relation between the pituitary and several metabolic variables. In a previous paper (Shapiro and Zwarenstein, 1933) the effect of hypophysectomy on the calcium content of the serum was reported. The prominent part played by the pituitary in regulating the water-salt content of the tissues was suggested by the work of Stehle (1926) on the diuretic-antidiuretic action of pituitary extracts. In Xenopus the low level of serum calcium which occurred as a result of pituitary re-moval was never associated with tetanic symptoms. These considerations and the well-known antagonism between calcium and potassium in all biological phenomena suggested an enquiry into the effects of hypophysectomy on serum potassium.
EXPERIMENTAL METHODS AND DATA
All the animals used in this investigation were females. The serum potassium was estimated by the micro-method of Dreguss (1931). 0·2 c.c. serum was used for each determination. One and occasionally two animals sufficed for each determination. Care was taken to collect the serum as soon as possible after the blood had coagulated, and in most cases it was possible to do this within 2 hours of collecting the blood. Added potassium was recovered from serum with errors of 3−6 per cent., and duplicate and triplicate estimations on the same sample of serum did not differ by more than 4 per cent.
It was pointed out in the previous communication that both captivity and hypophysectomy are associated with retrogression of the ovaries, the degree of which is correlated with the length of captivity and with the type of operation—whether removal of both lobes of the pituitary or of the anterior lobe alone. It was shown that regeneration of the pars tuberalis is associated with recovery of the white background response and a rise in serum calcium to normal, but that these effects were not associated with any regenerative effect on the ovaries. The serum potassium was therefore estimated in the following classes of animals: (i) normal toads after 2 months’ captivity ; (ii) normal after 7 months’ captivity ; (iii) toads with both lobes of pituitary removed; (iv) with anterior lobe alone removed (i.e. pars tuberalis and pars anterior) ; and (v) with regenerated pars tuberalis (melanophore index — 2). The hypophysectomised animals had been operated on 7-8 months previously.
DISCUSSION
The serum potassium after 7 months’ captivity is about 5 per cent, lower than after 2 months’ captivity. Statistical analysis of the two series of figures in Table I shows, however, that the difference between the two means is less than twice the standard deviation of the difference. The 5 per cent, decrease is, therefore, not necessarily significant.
Inspection of Table II shows that hypophysectomy leads to a fall in the potassium content of the serum of about 22 per cent. The figures for the various classes overlap to a certain extent. The differences in the means are slight and by no means as clear-cut as the corresponding calcium figures. Since the differences between the three series are not significant it can be concluded that the pars anterior is probably the main if not the sole constituent of the pituitary controlling the potassium content of the serum.
No certain correlation was found to exist between the degree of ovarian retro-gression 
and serum potassium. On the whole it was closer than the corresponding relation between ovarian involution and serum calcium. One outstanding difference emerges on comparing the influence of hypo-physectomy on serum calcium and potassium. Regeneration of the pars tuberalis is without effect on the involuted ovary. Similarly it is without effect on serum potassium but causes a rise in serum calcium to normal. It is probable that the influence of the pars anterior on ovarian activity and its influence on serum potassium are concomitant and parallel activities. A subsidiary correlation thus exists between serum potassium and ovarian activity. The evidence at present does not permit of any conclusion in regard to whether the influence of the pituitary on serum potassium is direct or indirect.
SUMMARY
Removal of both lobes of the pituitary gland, or of the anterior lobe (i.e. pars anterior and pars tuberalis) alone lead to a 22 per cent, fall in the potassium content of the serum.
Subsequent regeneration of the pars tuberalis has no effect on the lowered serum potassium level.
It is suggested that the pars anterior is the main constituent of the pituitary controlling, directly or indirectly, the potassium content of the serum.
ACKNOWLEDGEMENTS
The author wishes to thank Miss L. M. Starke for assistance in the potassium estimations. The expenses of this research were partly defrayed by a grant from the Medical Research Council to the Department of Social Biology.
