CHAPTER 22The Adrenal Medulla & Adrenal Cortex 357circulating angiotensinogen (see Chapter 39). Injections of an-
giotensin II stimulate adrenocortical secretion and, in small
doses, affect primarily the secretion of aldosterone (Figure
22–24). The sites of action of angiotensin II are both early and
late in the steroid biosynthetic pathway. The early action is on
the conversion of cholesterol to pregnenolone, and the late ac-
tion is on the conversion of corticosterone to aldosterone
(Figure 22–8). Angiotensin II does not increase the secretion of
deoxycorticosterone, which is controlled by ACTH.
Renin is secreted from the juxtaglomerular cells that sur-
round the renal afferent arterioles as they enter the glomeruli
(see Chapter 39). Aldosterone secretion is regulated via theFIGURE 22–22 “Escape” from the sodium-retaining effect of desoxycorticosterone acetate (DOCA) in an adrenalectomized patient. ECF,
extracellular fluid volume; TBV, total blood volume; RCV, red cell volume; PV, plasma volume. (Courtesy of EG Biglieri.)
150
100
50
06 Serum K+
(meq/L)Serum Na+
(meq/L)4DOCA 10 mg IM every 12 h3002001000150
130
IntakeIntake60
58
56Days 1Body weight
(kg)3 5 7 9 11 13 15 1711.40 L
4.26 L
1.14 L
3.12 L9.14 L
3.55 L
1.48 L
2.07 LECF
TBV
RCV
PVUrinary Na+
(meq/24 h)Urinary K+
(meq/24 h)Male, age 29
Bilateral adrenalectomy
Dexamethasone, 0.25 mg/6 hTABLE 22–6 Conditions that increase
aldosterone secretion.
Glucocorticoid secretion also increased
Surgery
Anxiety
Physical trauma
Hemorrhage
Glucocorticoid secretion unaffected
High potassium intake
Low sodium intake
Constriction of inferior vena cava in thorax
Standing
Secondary hyperaldosteronism (in some cases of congestive heart fail-
ure, cirrhosis, and nephrosis)FIGURE 22–23 Changes in adrenal venous output of
steroids produced by ACTH in nephrectomized
hypophysectomized dogs.12 40
10
Change in 8
17-hydroxy-
corticoid
output
(μg/min)Change in
aldosterone
output
(ng/min)6
4
2
030
25
20
15
10
5
0
2 5 10 100 1000
Dose of ACTH
(mU)
No. of dogs (4) (8) (6) (3) (10)