Catecholamines – Adrenal Pharmacology

00:01 The adrenal medulla is responsible for catecholamine production.

00:05 Because we already covered this in the autonomic nervous sytem section of pharmacology, we won't discuss it here.

00:16 There is one thing I want to mention however, with respect to the adrenal medulla.

00:20 I want to talk about a cancer or a lesion called pheochromocytoma.

00:26 Pheochromocytoma is a neuroendocrine tumour. It is often found in the adrenal gland but it can be found outside the adrenal gland as well.

00:35 It results in excess production of catecholamines, mostly norepinephrine.

00:40 We can do all kinds of tests. One of the most easy and simple test is the 24 hour metanephrine test of the urine.

00:47 We check for vanillylmandelic acid and metanephrines as a routine in a 24 hour test, but we can also do clinical testing and take a look at patients' blood pressure and heart rate and see that they tend to have very high levels.

01:02 Serum testing can also be done. It is exceedingly expensive, but it's highly accurate.

01:07 I rarely have done serum testing on patients when I'm diagnosing pheochromocytoma we've actually made a diagnosis just with the 24 hour urine and clinically, and we've had actually managed to remove successfully many pheochromocytomas.

01:23 Remember that plasma metanephrines can also be analyzed. We would be looking specifically for normetanephrine and metanephrine.

01:32 Treatment of pheochromocytoma is invariably surgical. We have to remove the tumour.

01:37 Now there are some pharmacological treatments that we do utilize. These are not permanent treatment therapies.

01:43 These are just hold over treatment therapies or bridge therapies.

01:46 Phenoxybenzamine, we've learnt about this drug in the CNS lectures, is a nonspecific irreversible alpha blocker.

01:56 A short acting alpha blocker is prazosin. We can also use terazocin as well.

02:03 Now, the other thing that we like to use is labetolol which has combined alpha and beta blocker activity to help us control the heart rate.

02:11 It's important that we never use a specific beta 1 blocker, because when you give a beta 1 blocker to a patient with pheo, you're gonna have unopposed alpha activity. And for the purposes of the exams, we're going to always say never use a specific beta 1 blocker.

02:30 In reality, sometimes we have, but I won't get into why, and I want you to forget what I just said.

02:35 On your exam, never use a beta 1 blocker, remember that part.

02:40 Now, in terms of volume repletion, remember that you want to give these patients fluids.

02:45 And sometimes we actually do something called "salt loading" in some patients.

02:49 That's a specific issue that we deal with in the pre-operative clinic.