Dec., 19511 j PICKFORD 681 Hypophysectomy in the Preparation of Mammals for the Bio-Assay of Adrenocorticotrophic Hormone Activity BY M. PICKFORD This paper formed the basis of an introductory address to four papers* o n the Biological Assay of Adrenocovticotrophic and Cortical Hormones @resented at the meetings of the Biological Methods Group on Tuesday, October 24th and Tuesday, December 19th, 1950. HYPOPHYSECTOMY is now frequently performed on a wide variety of vertebrate species as a preliminary to investigating the activities of other endocrines, and it is particularly needed before the bio-assay of adrenocorticotrophic hormones (ACTH). Removal of the pituitary is necessary because, in this instance, the endogenous production of ACTH interferes with the action of the ACTH injected for assay.For reasons of convenience, rats are frequently the animal of choice in large-scale assay work. They can be obtained easily, they are not large and a number can be kept in a small space, and they are remarkably resistant to infections, so that, provided reasonable cleanliness prevails at the operation, it is certain that no sepsis will result. This saves all the trouble involved in aseptic techniques. When performed by an expert the operation of hypophysectomy of rats appears easy. In fact it is not so, both innate skill and experience being necessary for its successful performance. The method generally used for hypophysectomising rats is in essence that described by Smith in 1927 and by Richter and Wislocki in 1930 and uses the parapharyngeal approach.The anaesthetic of choice is ether, despite the resulting free formation of fluid and mucus in the respiratory tract. Rats need large doses of atropine for even some control of this secretion and it is necessary to use suction as well t o keep the airways clear. Suction is also used for removal of the gland. It is possible to choose a suction tube whose tip is of such a size that the gland blocks the end, is held there and can be picked out and laid aside for examination later. There is little danger of injury to the hypothalamus because the rat, like man, has a diaphragm of dura across the sella between the pituitary and the base of the brain. It is advisable to keep the rats in a cage warmed to 28" C for some hours post-operatively, and the animals should never again be allowed to get cold.In expert hands mortality from hypophysectomy is nil and haemorrhage minimal. It takes 4 to 15 minutes to complete the operation without assistance. Hypophysectomised rats survive for long periods, although on the whole they do not live as long as normal ones. The two chief precautions needed to ensure survival are warmth, as they are unable to adapt well to low temperatures, and an always-available supply of food to reduce the risk of hypoglycaemia. A number of species may be hypophysectomised by a similar parapharyngeal route, including mice, ferrets, hedgehogs, guinea pigs and cats. With cats some workers prefer * Analyst, 1951, 76, 461-481.682 PICKFORD [Vol. 76 to use the buccal route and, in any event, the technique must be accompanied by thorough aseptic precautions, as cats tend to develop pneumonia. In certain species the buccal route is safer and easier than the parapharyngeal, for example, rabbits, fowls and dogs.From the first two the gland can be removed by suction, but for the last dissection is necessary. For total hypophysectomy in the dog it is not enough to remove all visible fragments of the gland, as the pars tuberalis runs up the stalk and spreads fanwise below the hypothalamus. The only certain way of destroying this part is by careful use of the thermocautery. Some injury to the hypothalamus cannot be avoided, but unless the pars tuberalis is destroyed the results of the operation are uncertain. A small viable portion of any part of the anterior lobe is enough to maintain the adrenals and the dog in almost normal condition.This must mean that the remaining fragment of gland is making an appreciable amount of ACTH. There is no diaphragm across the sella in the dog, so that some escape of cerebrospinal fluid is inevitable, but this seems to be of no moment. At the end of the operation plugging is unnecessary nor need the soft palate be stitched.. Infection is never seen unless the operator has been careless about asepsis. It is pleasing and surprising how little shock follows the buccal removal of the gland. The post-operative requirements are warmth, ample food and glucose added to the milk. The dog is generally well for the first one or two days, then less well and quieter. Later its condition again improves, but it is never as vigorous as before operation.The advantage of this method is that the stalk of the pituitary and the base of the hypothalamus can be seen. The disadvantages are that part of the zygorna has to be removed, the temporal muscle reflected, a large aperture made in the skull and the temporal lobes of the cerebrum retracted. This method, therefore, is followed by considerable operative shock and discomfort for the animal and needs far greater care as to asepsis. Before attempting hypophysectomy on any species it is advisable, and certainly helpful, to watch the performance of the operation by an expert. In dogs and monkeys the transtemporal route can be used. BIBLIOGRAPHY Allan, H., and Wiles, P., (Cats) J . Physiol., 1932, 75, 23. Dott, N. M., (Dogs) Quart. J . Exp. Physiol., 1923, 13, 241. Fisher, C., Ingram, W. R., and Ranson, S. W., (Cats, Monkeys) “Diabetes Insipidus,” Edwards Hill, M., and Parkes, A. S., (Ferrets, Hedgehogs, Guinea Pigs and Fowls) Proc. Roy. Soc. B, 1932, McPhail, M. K., (Cats) Ibid., 1935, 117, 45. Newton, W. H., (Rabbits) Endocrinology, 1939, 24, 468. Richter, C. P., and Wislocki, G. B., (Rats) A n w . J . Physiol., 1930, 95, 481. Smith, P., (Rats) J . Amer. Med. Ass., 1927, 58, 168. Sweet, J. E., (Dogs) Ann. Surgery, l.935, 102, 1069. Thompson, K. W. , (Rats) Endocrinology, 1932, 16, 257. White, E. W., (Rabbits) Proc. Roy. Soc. B, 1933, 114, 64. Bros. Inc., Ann Arbor, 1938. 112, 138. PHYSIOLOGY DEPARTMENT EDINBURGH UNIVERSITY