Evolution in vivo of the synthesis rate of catecholamines in various peripheral organs of the rat during cold exposure

The synthesis of catecholamines (CA) has been studied in the heart, spleen, submaxillary glands and adrenals of rats exposed to 4 degrees C for 2.5, 24 or 48 h. The synthesis rate has been estimated 30 min after an i.v. injection of 3H tyrosine (TY) by the evaluation of the ratio: 3H-CA specific activity/3H-TY specific activity. In the sub-maxillary glands, cold exposure reduced the noradrenaline (NA) synthesis by 40% at times 24 and 48 h. In the spleen, NA synthesis was multiplied by a factor 1.6 at times 2.5 and 24 h and 2.8 at time 48 h. In the heart, it was increased by a factor 1.3 after 2.5 h, 2.8 after 24 h and 5.5 after 48 h: an important fall in cardiac NA level was observed during the first 24 h of cold exposure indicating that the synthesis capability was unsufficient to compensate the cold-induced NA release. In the adrenals, adrenaline + NA synthesis was not significantly enhanced during the first 24 h of cold exposure and increased by a factor 2.4 at time 48 h. The important increases in CA synthesis which are observed during the 24-48 h interval are likely consecutive to the induction of tyrosine hydroxylase which has been reported in the rat exposed to cold.

The long term effects of an inhibitor of phenylethanolamine N-methyltransferase upon adrenal epinephrine biosynthesis

Chronic administration of SK&F 64139, an inhibitor of phenylethanolamine N-methyltransferase (PNMT), initially resulted in a lowered adrenal epinephrine content in both the rat and squirrel monkey adrenal gland. With continued dosing, however, these levels returned toward control. The latter changes were accompanied by increased adrenal levels of norepinephrine and PNMT, but not by decreased plasma drug levels. These results suggest that long-term pharmacological PNMT inhibition may evoke compensatory mechanisms to maintain adrenal epinephrine biosynthesis under basal laboratory conditions.

Studies on adrenal phenylethanolamine N- methyltransferase (PNMT) with S K & F 64139, a selective inhibitor

SK&F 64139 is a potent, reversible inhibitor of phenylethanolamine N-methyltransferase; its IC50 concentration in our standard assay system was 1 X 10(-7) M. Kinetically, the compound is a competitive inhibitor with respect to norepinephrine but is uncompetitive when S-adenosylmethionine is the variable substrate. In contrast to a previously reported compound (SK&F 7698), the drug is only a weak alpha receptor antagonist (KB = 6 X 10(-6) M). In both the rat and squirrel monkey, SK&F 64139 produced dose-dependent decreases in the adrenal epinephrine content coupled with stoichiometrically equivalent increases in the norepinephrine pool(s). Further evidence for in vivo phenylethanolamine N-methyltransferase inhibitory activity was that the drug markedly inhibited the conversion of a tracer dose of 3H-norepinephrine to 3H-epinephrine in the rat adrenal gland after unit oral doses as low as 5 mg/kg.

Lack of epinine formation in adrenal medulla and brain of rats during cold exposure and inhibition of dopamine beta-hydroxylase

Cold exposure of rats for 4 h and simultaneous inhibition of dopamine beta-hydroxylase by FLA-63 (25mg/kg) led to a reduction of the catecholamine content of the adrenal medulla by 46% and of the brain by 68%. Additional injections of 5 mg/kg FLA-63 4 and 9 h after beginning of the experiments, respectively, kept the catecholamine content on this low level (brain) or decreased it further (adrenal medulla). Administration of 5 mg/kg (-)DOPA together with the mono-amine oxidase inhibitor pargyline (50 mg/kg) 24 h after the first injection of FLA-63 stimulated the resynthesis. It amounted for the adrenal medulla to 20 mug/kg body weight/8 h and for the brain to 45ng/g tissue wet weight/8 h. Paper chromatographic analyses of the extracts of adrenal medulla and brain, respectively, performed at each time of the different injections, clearly identified adrenaline, noradrenaline and dopamine (in traces) in the adrenal medulla as well as noradrenaline and dopamine in the brain; epinine on the contray could not be demonstrated, not even in traces. Since at least 25 ng of epinine can be detected with certainty by our method, it can be concluded that epinine is not formed in amounts greater than 75 ng/pair adrenal glands or 37.5 ng/brain. The present results support the view that the main pathway of adrenaline biosynthesis in the suprarenal medulla and the brain proceeds via noradrenaline and not via epinine.

Observations on the localization of recently synthesized catecholamines in chromaffin cells after the injection of L-(2,5,6-3H)dopa

The fate of tl-[2, 5, 6-3h] dopa, and the intracellular localization of its metabolic products dopamine, noradrenaline and adrenaline, have been determined by the simultaneous use of assay techniques following separation of amines by chromatography and light and electron microscopic autoradiography. During the first 24 h after i.v. or i.p. injection of [3H] DOPA, synthesis of the above catecholamines occurred. Throughout this time the labelled amines were associated with chromaffin granules or immediately adjacent cytosol and not with either the Golgi complex or rough endoplasmic reticulum. Labelling of chromaffin granules occurred simultaneously throughout the cell and there was no evidence of regions containing recently labelled granules and others containing previously charged (older) granules. Adrenaline-storing cells took up [3H] DOPA and its products more rapidly and lost recently synthesized adrenaline more rapidly than noradrenaline-storing cells took up and stored their equivalent amines. This was in keeping with a more rapid turnover of catecholamines in adrenaline-storing elements.

Synthesis of catecholamines in the eye after local injection of 3H-precursors

The possibility that adrenaline may be synthesized locally in the eye was investigated in the rabbit and vervet monkey. L-tyrosine-3,5-3H, L-tyrosine (side-chain-2,3-3H) or L-3,4-dihydroxyphenylalanine (3H(G)) was injected into the anterior chamber or the vitreous. The animals were killed after 1/2 h up to 7 days in the tyrosine experiments and after 1 up to 24 h in the DOPA experiments. The synthesis of 3H-adrenaline, 3H-noradrenaline and 3H-dopamine was measured with a modified version of a double isotope technique for determination of catecholamines. No 3H-adrenaline was found. An attempt to stimulate the phenylethanolamine-N-methyltransferase activity with a glucocorticoid and to inhibit the metabolism of catecholamines with a monoaminoxidase inhibitor also failed to demonstrate 3H-adrenaline synthesis. 3H-noradrenaline was found in all experiments when 3H-DOPA had been given. The amounts were about 10 times higher after injection into the anterior chamber than after injection into the vitreous. 3H-dopamine was found in all except a few experiments after 3H-DOPA injection. The highest amounts were found after injection into the vitreous. In experiments with 3H-tyrosine we were unable to demonstrate any catecholamine synthesis. This prompts the question of whether tyrosine-hydroxylase may be absent in the eyes of certain animal species.

[Mechanisms of catecholamine synthesis disorders in the adrenals of rats subjected to physical fatigue]

There was a depression of transformation of noradrenaline, DOPA and thyrosine added in vitro, into catecholamines in the adrenal glands of rats after swimming for a period of 8 hours. This permitted to suppose a depression of the activity of phenylethanolamine-N-methyl-transpherase, DOPA-decarboxylase, and, possibly, of tyrosine hydroxylase under these conditions. After the end of swimming, in the presence of 1-tyrosine, there is at first an activation of noradrenaline synthesis, and then there occurs a gradual normalization (on the 7th day) of adrenaline formation. In rats trained for a period of 2 months the extent of reduction of the catecholamine synthesis in the adrenal glands in response to the 8-hour swimming was much less in comparison with the untrained aniamals.

Studies on the synthesis and subcellular distribution of dopamine in the rat adrenal medulla

Rats received intravenous injections of 3H-tyrosine and were killed at various time intervals thereafter. 3H-dopamine (DA) in the adrenals reached a maximum within 1.5 min after the administration of 3h=tyrosine. From the 15th min it disappeared with an apparent half life of 90 min. 3H-Adrenaline (A) plus 3H-noradrenaline(NA) increased much more slowly and reached a plateau 120-240 min after the injection. The approximate synthesis rate of adrenal A plus NA, calculated from the specific activity curves, ranged from 0.3 to 2.2 nmoles/h per kg b.w. The highest value was noted the first few minutes, the lowest 1-2 hrs after the administration of 3H-tyrosine. In some experiments subcellular fractionation of the adrenals was performed. In untreated animals the amount of DA and A plus NA recovered from the supernatant fraction was about 10 and 8 per cent, respectively, of the total amount recovered from the supernatant and particulate fractions. In the adrenals of animals receiving 3H-tyrosine 3.75 or 60 min beforehand these figures were significantly elevated whereas the DA and A plus NA of the particulate fraction did not deviate significantly from control values. The specific activities of 3H-DA were the same in the supernatant and particulate fractions within 3.75 min after the injection of 3H-tyrosine.