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An attempt has been made to determine the relative functional activities of adrenal and extra-adrenal chromaffin tissue during the neonatal phase and up to 1 week of age using young rabbits and guinea-pigs whose main extra-adrenal abdominal para-aortic chromaffin bodies are respectively non-innervated and innervated. Amine synthesis and storage were followed by assay and autoradiography after a single intraperitoneal injection of L-[2,5,6-3H]DOPA and the findings correlated with amine content as assessed by high performance liquid chromatography and by volume of tissue. The results indicate that in the guinea-pig, in spite of differences in proportions of adrenaline and noradrenaline in the adrenal gland and para-aortic body (PAB), the loss of labelled catecholamines from the innervated PAB closely follows that from the adrenal medulla, suggesting that both participate in normal sympathoadrenal activity. By comparison, in the rabbit the PAB shows only a minimal decreased labelled amine during the first week of life during which period the amine content and concentration of the PAB doubles: the functional significance of this non-innervated extra-adrenal chromaffin tissue, which persists throughout life, has still to be determined.

Using morphometric analysis and high-pressure liquid chromatography with electrochemical detection of catecholamines the volumes of adrenaline-storing (A) and noradrenaline-storing (NA) cells and the adrenaline and noradrenaline contents of adrenal glands of normal and age-matched hypophysectomized rats were determined and compared. Some hypophysectomized rats were also administered 150 mg metyrapone/kg daily for a 4-week period. Hypophysectomy resulted in an increase in noradrenaline storage in adrenal glands. This was more marked in hypophysectomized animals not treated with metyrapone even though the combination of metyrapone and hypophysectomy resulted in a reduction of blood corticosterone concentration to only approximately 6% normal. There was no evidence of a change in proportion of A and NA cells in the adrenal medulla of hypophysectomized rats or hypophysectomized animals treated with metyrapone and it is concluded that the changes in amine concentrations and proportions observed reflect an increase in the storage of noradrenaline in A cells as a consequence of less efficient methylation of noradrenaline after hypophysectomy. The findings also showed that the left adrenal gland and medulla was usually slightly larger and had a greater catecholamine content and slightly higher proportion of NA cells than the right adrenal gland. During the period of the experiment (animals aged 6-15 weeks) there was an increase in the concentration of both adrenaline and noradrenaline in the normal adrenal glands. In normal Sprague-Dawley rats weighing 140 and 400 g the adrenal medulla accounted for some 5% of adrenal volume; this increased to 13% after hypophysectomy; A and NA cells together accounted for 50-60% of the volume of adrenal medulla.

A descriptive account and morphometric study of the adrenal medulla and adrenal chromaffin cells of Wistar rats aged from birth to 22 months is presented. Distinct adrenaline and noradrenaline-storing types of chromaffin cells are first identified in 4-day-old animals, prior to that time individual cells contain both adrenaline- and noradrenaline-storing granules. Primitive sympathetic cells and phaeochromoblasts occurs up to 2 days postnatally. Mitotic figures occur in chromaffin cells of a maturity and appearance appropriate to age and most frequently in adrenaline-storing cells. The adrenal medulla continues to increase in volume throughout the period and chromaffin cells increase in number and in some cases volume. There is a corresponding increase in neuronal elements. In 22-month-old rats individual cells or groups of chromaffin cells show evidence of hypertrophy and changes in cytoplasmic organelles, in particular lysosomes, rough endoplasmic reticulum and storage granules and vesicles. Some hypertrophied chromaffin cells contain a heterogeneous population of granules suggesting a degree of functional plasticity in some cells in aged rats.

Light-microscopic autoradiography has revealed characteristic labelling patterns in adrenal medullary cells following the intravenous administration of different catecholamines. The uptake patterns for [3H] dopa, [3H] dopamine, [3H] noradrenaline and [3H] adrenaline ahve been compared. In all cases A cells were more active than NA cells and cells situated in the zone nearest the cortex demonstrated a markedly higher rate of uptake than central cells. It was concluded that adjacent chromaffin cells with very similar morphology may differ as much as 50 fold in their capacities to incorporate exogenous amines. The adrenergic nature of te innervation of the vessels of the adrenal cortex and capsule in the mouse was confirmed.

Following intravenous or intraperitoneal injections of 3H-l-dopa radioactivity in adrenal medullary chromaffin cells of the mouse has been followed by autoradiographic and radioisotopic assay methods. For autoradiographic purposes tissues were fixed in either phosphate buffered glutaraldehyde or in 1-5% potassium dichromate in glutaraldehyde pH 7-2. A high initial radioactivity is demonstrated by both autoradiography and radioisotopic assay. During the first hour dopamine is the predominant labelled amine. Between 1 and 4 hours after the injection noradrenaline is in highest concentration and from 1 to 24 hours labelled adrenaline appears and becomes the predominant labelled amine (about 70%) after 24 hours. Autoradiographs of tissues fixed in glutaraldehyde alone confirm that adrenaline is lost from sections by this technique. When 1-5% potassium dichromate is added to glutaraldehyde then adrenline is fixed in A cells and these show only a slightly decreased grain count as compared to NA cells at 5 days; this slight decrease is probably due to more rapid turnover of amines by A cells.

An autoradiographic study was performed on the effects of hydrocortisone, reserpine, propranolol and phentolamine on the uptake of tritiated amines by adrenal medullary cells of the mouse. Oral feeding of hydrocortisone ahd no significant effect on the normal uptake pattern of dopamine, noradrenaline or adrenaline by medullary cells of different type (A cells or NA cells) or location (marginal or central), although the overall amounts taken up were markedly reduced. Handling the animals led to similar reductions in the uptake of all three amines and was thus clearly shown to be the important factor in this effect. Reserpine reduced the uptake of [3H] noradrenaline to 25% of the control value although the relative distribution remained unchanged. Propranolol and phentolamine had no observed effect on [3H] noradrenaline uptake. These results are discussed in the light of the previously reported action of ACTH in reversing the effects of hypophysectomy on medullary amine uptake (Hirano and Kobayashi 1978), and it is concluded that ACTH must exert this effect directly on the adrenal medulla rather than through the secretion of adrenal corticosteroids. It is also suggested that reserpine acts, as in neurons, by blocking amine uptake into intracellular granules rather than by blocking uptake into the cell itself.