Pharmacology Biochemistry & Behavior, Vol. 6, pp. 145--149. Copyright © 19"77 by ANKHO International Inc. All rights of reproduction in any form reserved. Printed in the U.S.A.

Adrenergic Stimulation of the Lateral Hypothalamic Area on Sodium and Potassium Excretion A L I C E X. P I L L A R 1 , C I N C I N A T O R. S I L V A - N E T T O , L U I Z A. A. C A M A R G O 2 , W I L S O N A. S A A D 2, J O S E A N T U N E S - R O D R I G U E S A N D M I G U E L R. C O V I A N .

Department o f Physiology, School o f Medicine, 14.100 Ribeirao Preto, SP, Brasil ( R e c e i v e d 12 O c t o b e r 1976) PILLAR, A. X., C. R. SILVA-NETTO, L. A. A. CAMARGO, W. A. SAAD, J. ANTUNES-RODRIGUES AND M. R. COVIAN. Adrenergic stimulation of the lateral hypothalamic area on sodium and potassium excretion. PHARMAC. BIOCHEM. BEHAV. 6(2) 145-149, 1977. - The effects of adrenergic stimulation of the lateral hypothalamic area on sodium and potassium excretion were studied in rats bearing implanted cannulae. When noradrenaline was injected into several points of the lateral hypothalamic area, a dose-related increase in natriuresis and kaliuresis was observed. Rats previously injected through the same cannulae with c~ (Regitine) or ~ (Propranolol) blocking agents showed different natriuretic responses when injected with noradrenaline. It was observed that the normal noradrenaline-induced natriuresis was abolished by the a-adrenergic blockers, while/3-adrenergic blockers increased the response. Intrahypothalamic injection of Isoproterenol, an activator of the ~-adrenergic receptor, induced a decrease in natriuresis, kaliuresis and urinary volume. In contrast, injection of Metaraminol, an c~-adrenergic agonist, caused an increase in sodium and potassium excretion and a reduction of urinary volume. Drugs blocking the destruction of noradrenaline or its reuptake by the presynaptic nerve endings potentiated 2-fold the action of 20 nmol of noradrenaline. These experiments provide good evidence for the existence of an adrenergic mechanism consisting of c~ and ~/ receptors which works antagonistically on the regulation of sodium and potassium excretion. The excretion of the two electrolytes is stimulated by the a-adrenergic system, and inhibited by the ~-adrenergic system. Adrenergic stimulation

Lateral hypothalamic area

Electrolytes excretion

Silva-Netto et al. [23] d e m o n s t r a t e d the relative participation of t h e h y p o t h a l a m u s - h y p o p h y s i s system in the increase of Na + and K + e x c r e t i o n by i n j e c t i n g c a r b a c h o l i n t o the lateral h y p o t h a l a m i c area of h y p o p h y s e c t o m i z e d or m e d i a n e m i n e n c e lesioned rats. C a m a r g o et al. [ 5] have studied the role p l a y e d by the adrenergic p a t h w a y s in the septal area in the r e g u l a t i o n of e l e c t r o l y t e a n d w a t e r e x c r e t i o n , d e m o n s t r a t i n g t h a t the s t i m u l a t i n g a n d i n h i b i t i n g effects are m e d i a t e d , respectively, by the a and 13 adrenergic receptors. C o n s i d e r i n g these findings, it s e e m e d of i n t e r e s t to us to investigate t h e possible p a r t i c i p a t i o n of the adrenergic p a t h w a y s in the h y p o t h a l a m i c area in the r e g u l a t i o n of Na + and K + e x c r e t i o n a n d u r i n a r y v o l u m e , t h u s investigating the existence o f a neural circuit in this r e g u l a t o r y m e c h a n i s m similar to t h a t already d e t e r m i n e d for s o d i u m i n t a k e [ 8 ] .

A S E R I E S of i n v e s t i g a t i o n s h a s b e e n d e v o t e d to d e m o n strating t h e p a r t i c i p a t i o n of the c e n t r a l n e r v o u s system in the r e g u l a t i o n of the h y d r o m i n e r a l e q u i l i b r i u m of the organism. Many a u t h o r s have s t u d i e d t h e effects p r o d u c e d by c h e m i c a l or electric s t i m u l a t i o n , or by e l e c t r o l y t i c d e s t r u c t i o n of several areas in t h e limbic s y s t e m on water, f o o d a n d s o d i u m i n t a k e . It has b e e n r e p o r t e d t h a t the p r e o p t i c lateral area plays a role in w a t e r e q u i l i b r i u m in the organism, w h e n an a l t e r a t i o n occurs in the o s m o l a r i t y of the e x t r a c e l l u l a r fluid [ 3 , 4 ] . E x t e n s i v e research has b e e n carried o u t r e c e n t l y w i t h the p u r p o s e of p r o v i n g a possible p a r t i c i p a t i o n of the l i m b i c area in the r e g u l a t i o n of u r i n a r y e x c r e t i o n of s o d i u m , p o t a s s i u m and water. Early w o r k s in this field have s h o w n an increase in n a t r i u r e s i s a f t e r a lesion in the p a r a v e n t r i c u l a r nuclei [ 1 6 ] , p r e o p t i c area [ 1 7 ] , and the p o s t e r i o r h y p o t h a l a m u s [ 7 ] . H y p e r t o n i c s o l u t i o n of NaC1 (0.58 M) i n j e c t e d i n t o the t h i r d v e n t r i c l e of goats also caused an increase in natriuresis [ 1 ] . V e n t r i c u l o cisternal p e r f u s i o n w i t h l o w - s o d i u m s o l u t i o n decrease s o d i u m excret i o n [ 19]. Cholinergic s t i m u l a t i o n of various h y p o t h a l a m i c [6] a n d v e n t r i c u l a r [ 11 ] areas, as well as of t h e septal area [22] in rats p r o v o k e d an increase in the u r i n a r y e x c r e t i o n of s o d i u m a n d p o t a s s i u m a n d a decrease in u r i n a r y v o l u m e .

METHOD

Cannulae implanted into the lateral hypothalamie area (L.H.A.). H o l t z m a n a l b i n o rats weighing b e t w e e n 2 0 0 and 3 0 0 g were used in all e x p e r i m e n t s . Stainless steel c a n n u l a e were i m p l a n t e d i n t o the LHA of all a n i m a l s u n d e r e t h e r anesthesia, a c c o r d i n g to the s t a n d a r d s t e r e o t a x i c t e c h n i q u e based o n t h e c o o r d i n a t e s of t h e De G r o o t [10] atlas. The

Department of Physiology, Federal University of Santa Maria, 97.100 Santa Maria, Rio Grande do Sul, Brasih 2 Department of Physiology, School of Dentistry and Pharmacy, 14.800 Araraquara, SP, Brasil. 145

P I L L A R , E T AL.

146 c a n n u l a e were fixed to t h e skulls w i t h d e n t a l c e m e n t and j e w e l e r ' s screws. To p r e v e n t i n f e c t i o n , a t r e a t m e n t w i t h penicillin for 3 days b e f o r e a n d a f t e r the o p e r a t i o n was done. A f t e r cerebral surgery, the animals were r e t u r n e d to t h e i r o w n individual m e t a b o l i c cages and fed with pellets a n d tap w a t e r u n t i l the day of the e x p e r i m e n t ( o n e week later). A p o l y e t h y l e n e t u b e , to be used l a t e r for a d m i n i s tering w a t e r loads, was placed daily i n t o the s t o m a c h for 7 days, so t h a t t h e y w o u l d get a c c u s t o m e d to the experimental conditions. Experimental procedure. A f t e r a 14 hr p e r i o d o f f o o d d e p r i v a t i o n , the a n i m a l s were weighed and s u b m i t t e d to a first w a t e r load, w i t h w a t e r at 37°C, and in a q u a n t i t y equal to 5~7c of the a n i m a l ' s b o d y weight. The animals were t h e n r e t u r n e d to t h e i r cages and left w i t h o u t w a t e r and solid food. V o i d e d urine passed t h r o u g h the f u n n i l at the b o t t o m of the cage i n t o a g r a d u a t e c e n t r i f u g e t u b e . A f t e r 60 m i n u t e s , a similar s e c o n d w a t e r load was a d m i n i s t e r e d a n d the first urine sample was collected and dismissed. T w e n t y m i n u t e s later, a c o n t r o l urine sample was collected, and 1 /11 of saline s o l u t i o n (0.15 M NaC1) or the drug was i n j e c t e d into the LHA. A f t e r the i n j e c t i o n , 6 m o r e successive urine samples were collected at 20 rain intervals for a p e r i o d of 2 hr. Drugs. N o r a d r e n a l i n e (Sigma C h e m i c a l Co.), P r o p r a n o l o l h y d r o c h l o r i d e (Sigma Chemical Co.), Regitine (Ciba), lsop r o t e r e n o l h y d r o c h l o r i d e (Sigma C h e m i c a l Co.), Metar a m i n o l ( W i n t h r o p L a b o r a t o r i e s ) , Xilocaine - 2% (Astra L a b o r a t o r i e s , Brazil -- 1 /~1) and Nialamide (Sigma C h e m i c a l Co.). F o r the i n t r a c e r e b r a l injections the drugs were dissolved i n t o a 0.15M NaC1 s o l u t i o n . The i n j e c t i o n s (all o f t h e m 1 /~I in v o l u m e ) were m a d e t h r o u g h a m i c r o s y r i n g e ( H a m i l t o n Co.) fitted w i t h a 30 gauge needle, t h r o u g h PE 10 p o l y e t h y l e n e tubing, over a p e r i o d of 10 sec. A delay of at least 48 h r i n t e r v e n e d b e t w e e n tests in a given rat. In occasional i n s t a n c e s a drug was tested twice in t h e same animal. T h e r e was n o d e t e c t a b l e e f f e c t of p r i o r t r e a t m e n t s on t h e responses. All the drug doses used have b e e n expressed in n m o l , with the e x c e p t i o n of Lidocaine, w h i c h was 1 /11 of a 2% solution. Determination o f Na + and K +. The s o d i u m and potassium c o n c e n t r a t i o n s for each u r i n e sample were d e t e r m i n e d with a IL-143 flame s p e c t r o p h o t o m e t e r ( I n s t r u m e n t a t i o n Laboratories). Histology. A f t e r the e x p e r i m e n t s , t h e brains of all animals were r e m o v e d u n d e r anesthesia a n d fixed in 10% f o r m a l d e h y d e s o l u t i o n . Later the brains were cut in 10/J sections and stained by the g a l o c y a n i n e and Pal-Weigert t e c h n i q u e m o d i f i e d by E h r a r t [ 1 2 ] . Only the animals whose c a n n u l a e were f o u n d to be placed in t h e LHA were used for analysis of the data. Statistics. The S t u d e n t ' s t test was applied. The doseresponse curve was s u b m i t t e d to variance analysis and calculated linear regression. All data are expressed as average -2-- SEM.

RESULTS Effects o f the injection o f various noradrenaline doses into the LHA on the urinary excretion o f Na + and K +. Dose-response curve. T h e i n t r a c e r e b r a l i n j e c t i o n of 2.5, 5.0, 10, 20, 4 0 a n d 80 n m o l of n o r a d r e n a l i n e p r o v o k e d a dose-related increase in the u r i n a r y e x c r e t i o n of s o d i u m and p o t a s s i u m in a g r o u p of rats (Fig. 1). V a r i a n c e analysis s h o w e d a significant regression for s o d i u m in r e l a t i o n to the d i f f e r e n t doses applied, b u t n o significant deviation in

500

(11)

A 4,?.0

,g

(13)

NO+

340

,~

zso

I--

180

(12)//"

100 (1 20

I 2,5

~

K+

"

I 5

~

I I0 DOSE

I

20

T

I 40

I 80

(nmoO

FIG. I. Linear regression of the dose-response curve for the different doses of noradrenaline on sodium and potassium excretion. In parentheses, the number of rats.

linearity ( F 11.76 for Na+). The general regression equation for Na + was y = 6 4 . 6 4 + 74.11x. The e x c r e t i o n of K + increased in direct p r o p o r t i o n to the a m o u n t s of n o r a d r e n a l i n e up to 10 n m o l . B e y o n d this dose the e x c r e t i o n r e m a i n e d c o n s t a n t , s h o w i n g t h a t 10 n m o l are sufficient to activate all the r e c e p t o r s c o n n e c t e d with K + e x c r e t i o n . Variance analysis of regression for K* s h o w e d significant regression up to the 10 n m o l dose (y = 2 1 . 5 9 + 22.97x). B e y o n d this dose the regression was n o t significant (y = 124.51 - 0.52x). Table 1 shows t h e t i m e course and m a g n i t u d e of the typical n o r a d r e n a l i n e - i n d u c e d natriuresis and kaliuresis by intervals of t w e n t y m i n u t e s in c o m p a r i s o n w i t h results o b t a i n e d after i s o t o n i c saline i n j e c t i o n i n t o the LHA. A f t e r i n j e c t i o n of n o r a d r e n a l i n e ( 2 0 n m o l ) into the LHA the natriuresis rose rapidly, r e a c h e d a m a x i m u m at 60 rain later, t h e n declined. W h e n c o m p a r e d w i t h baseline levels of 0.42 -+ 0 . 0 5 / ~ E q / m i n , this r e p r e s e n t s a b o u t a 8-fold increase in u r i n a r y sodium, while K + increases was of less i n t e n s i t y . I s o t o n i c saline did n o t i n d u c e a n y change. Effects o f sympatholytic drugs on the increase o f urinary excretion o f Na + and K + induced by in/ection o f noradrenaline into the LHA metararninol and isoproterenol agonisrn. The i n j e c t i o n of 20 n m o l of n o r a d r e n a l i n e i n t o the LHA i n d u c e d a m a r k e d increase in the renal e x c r e t i o n of Na + and K + d u r i n g a p e r i o d of 2 h o u r s a f t e r the drug was a d m i n i s t e r e d , an effect similar to t h a t o b t a i n e d by injecting n o r a d r e n a l i n e i n t o the septal area [ 5 ] . The i n t r a h y p o t h a l a m i c i n j e c t i o n of 100 n m o l of Prop r a n o l o l 30 rain before i n t r a c r a n i a l i n j e c t i o n of n o r a d r e n a line caused a significant increase in the n a t r i u r e t i c effect p r o v o k e d by a d m i n i s t e r i n g 20 n m o l of n o r a d r e n a l i n e i n t o the LHA. In c o n t r a s t , i n t r a h y p o t h a l a m i c i n j e c t i o n of 20

LHA AND ELECTROLYTES

EXCRETION

147

TABLE

1

SODIUM AND POTASSIUM EXCRETION AND URINE VOLUME PLOTTED AS FUNCTION OF TIME, BY 20 MIN INTERVALS, BEFORE AND AFTER INJECTIONS OF THE TEST SOLUTIONS, ISOTONIC SALINE (0.15 M) OR NORADRENALINE (20 NMOL), INTO THE LATERAL HYPOTHALAMIC AREA -20

~

20

40

60

80

100

120min

Isotonic saline Na + (~Eq/min) K + (#Eq/min) Urine vol. (ml/20 min)

0.26 _ 0.02 0.50 ± 0.03 1.75 ± 0.10

0.26 ± 0.03 0.44 _+ 0.03 2.05 ± 0.13

0.27 ± 0.02 0.47 ± 0.03 2.51 _+ 0.13

0.32 - 0.01 0.50 ± 0.03 2.92 ± 0.12

0.25 ± 0.01 0.43 ± 0.03 2.52 _+ 0.13

0.23 _+ 0.02 0.39 ± 0.03 2.04 ± 0.13

0.22 ± 0.02 0.34 _+ 0.03 1.84 ± 0.11

Noradrenaline Na ÷ (#Eqlmin) K+(/~Eq/min) Urine vol. (ml/20 min)

0.42 ± 0.05 0.69 -- 0.05 1.94 _+ 0.12

1.78 _+ 0.23 0.74 ± 0.09 1.58 ± 0.16

2.78 _+ 0.23 1.14 + 0.10 1.74 _+ 0.18

3.39 _+ 1.24 1.11 + 0.08 2.30 _+ 0.14

1.25 ±0.14 0.86 _+ 0.09 2.24 _+ 0.16

0.64 +_ 0.05 0.61 _+ 0.05 2.25 ± 0.14

0.60 _+ 0.07 0.75 _+ 0.04 2.01 _+ 0.14

Each value represents the m e a n ± SEM, obtained in 20 rats. Baseline values are those obtained at - 2 0 min relative to injection of test solutions (arrow). Noradrenaline was injected 48 hr after isotonic saline.

2)"

200-

I250

I

DO.~

+

M NoCl

I

350-

D

PROPRANOLOL+NORA0~ENALINE (~OOnmol) (20 nmo0

D

METARAMINOL (20 nmol)

D

1 ~ 2OR~n mTE°IR~N OL

300-

RATS I i0

3 -150

Rt

~.

S o

250-

~

1

o

[ [~ ~ ~

~ ] 0 . 1 5 M NaQ

-200

ua tSO-

"~O

RATS = I0

~o

___--

100-

-300

LIDOCAINE (2%-tV0 NIALAM(~ (Z00 nmol) NORADRENALINE (20 nrf~)

-250

UDOCAINE+ NORADRENALINE (2%} (20 nmol) -'-~NIALAMIOE+ NORADRENALINE ( ~ ) (20 n m d ) -200

2OO-

Y~ =

cc bJ 50-

-50

~o-

-150 o

P, FIG. 2. Effects of adrenergic stimulation and adrenergic blocking o f the h y p o t h a l a m u s on sodium and potassium excretion. The values represent the m e a n ± SEM. nmol of Regitine before administering the agonist provoked a m a r k e d d e c r e a s e in t h e n a t r i u r e t i c e f f e c t . T h e i n j e c t i o n o f 20 n m o l o f I s o p r o t e r e n o l , a 13-adrenergic s t i m u l a n t , i n t o t h e L H A c a u s e d a s i g n i f i c a n t d e c r e a s e in r e n a l e x c r e t i o n o f Na ÷ a n d K + in c o m p a r i s o n w i t h t h e e f f e c t s o f b o t h s a l i n e a n d n o r a d r e n a l i n e i n j e c t i o n s . In contrast, the injection of 20 nmol of Metaraminol, an a - a d r e n e r g i c s t i m u l a n t , c a u s e d a n i n c r e a s e in t h e e x c r e t i o n o f Na + a n d K + (Fig. 2).

Effects o f intrahypothalamic in/ection o f drugs influencing the metabolism and recaptation o f noradrenaline in nerve endings on the renal elimination o f Na + and K +. T h e i n j e c t i o n o f 1 /ll o f L i d o c a i n e a t 2% i n t o t h e L H A c a u s e d a s i g n i f i c a n t i n c r e a s e in t h e u r i n a r y e x c r e t i o n o f N a + a n d K + in r e l a t i o n t o t h e c o n t r o l levels o b t a i n e d w i t h saline injection. Lidocaine injected 50 rain before the injection of 20 n m o l o f n o r a d r e n a l i n e p r o v o k e a s i g n i f i c a n t i n c r e a s e in t h e

-~o ~?

I00,///

50-

,/H

)

.

: ~ ..... - ~

-50

FIG. 3. Effects on sodium and potassium excretion of intrahypothalamic injections of the agents acting on noradrenaline metabolism and recaptation. The values represent the m e a n ± SEM. n a t r i u r e t i c a n d k a l i u r e t i c e f f e c t o f t h e a d r e n e r g i c agonist. The injection of 200 nmol of nialamide determined an i n c r e a s e in t h e u r i n a r y e x c r e t i o n o f t h e t w o e l e c t r o l y t e s when compared with saline injection. Nialamide given 50 min prior to intrahypothalamic injection of 20 nmol n o r a d r e n a l i n e o n c e m o r e p r o v o k e d a m a r k e d i n c r e a s e in t h e u r i n a r y e x c r e t i o n o f N a + a n d K +, w h e n t h e s e e f f e c t s are

P I L L A R , E T AL.

148

A5.8

AT.0

I "T

A6.6

I I

A 6.2

A7.4

¢Pu

I L~

I DI se.

,, *

US

¢PU iv

",:,. ~

•

_

_

".

a

Qp

I

¢,

"',i "'x

:."

., E ' , - , ' " ; '

,,,

,',

..,

:' ,

[]

, ~

...

"

m,

,, .

-..--."

%'

,o

.' ~ , .

,

.o- t J .• i" , ,

,1.I o~ . I~/ Zi

.

,J

15-:e::.o It L ~

~t

'. ~ AM[

*

L

FIG. 4. Loci of stimulation shown on sections from the rat brain, based on the De Groot's atlas [10]. The open circles indicate consistently excellent effects of adrenergic stimulation on the increase of sodium and potassium excretion; the half-filled circles show the placements with some effects; the open squares indicate negative placements. c o m p a r e d with t h o s e of saline or n o r a d r e n a l i n e alone (Fig.

3). Localization o f the implanted cannulae. Figure 4 shows the p l a c e m e n t of the c a n n u l a e in f r o n t a l section. The o p e n circles i n d i c a t e the p o i n t s where the adrenergic s t i m u l a t i o n was effective in s t i m u l a t i n g s o d i u m a n d p o t a s s i u m excretion. It m a y be n o t e d t h a t m o s t of the loci are c o n c e n t r a t e d i n t o the lateral h y p o t h a l a m i c area b e t w e e n the a n t e r i o r and the m e d i a n h y p o t h a l a m u s . DISCUSSION

T h e p r e s e n t results i n d i c a t e t h a t the LHA p a r t i c i p a t e s in the neural r e g u l a t o r y c o n t r o l of u r i n a r y s o d i u m a n d p o t a s s i u m e x c r e t i o n w h e n its adrenergic p a t h w a y s are s t i m u l a t e d . The a d m i n i s t r a t i o n of n o r a d r e n a l i n e i n t o this area p r o v o k e d a progressive, d o s e - d e p e n d e n t increase in the u r i n a r y o u t p u t of s o d i u m and p o t a s s i u m . The effects of n o r a d r e n a l i n e on p o t a s s i u m e x c r e t i o n are m o r e rapid and less intense, with a p l a t e a u being r e a c h e d earlier t h a n for sodium. T h e 20 n m o l dose c h o s e n for s o d i u m e x c r e t i o n is a m a x i m u m dose for p o t a s s i u m e x c r e t i o n , w h i c h p r o b a b l y p r e v e n t s any possible p o t e n t i a t i o n of its effects. On the o t h e r h a n d , k n o w i n g t h a t n o r a d r e n a l i n e acts t h r o u g h c~ a n d adrenergic r e c e p t o r s , we a t t e m p t e d to verify w h e t h e r its effects were m e d i a t e d p r e f e r e n t i a l l y by one or the o t h e r of the t w o p a t h w a y s . The i n j e c t i o n of n o r a d r e n a l i n e i n t o animals previously i n j e c t e d with the 13-adrenergic a n t a g o n i s t P r o p r a n o l o l d e t e r m i n e d a p o t e n t i a t i o n o f effects. However, w h e n an a n i m a l previously t r e a t e d with Regitine (an c~-adrenergic b l o c k i n g agent) was injected with c a t e c h o l a -

mine an i n t e n s e decrease of the effects n o r m a l l y o b t a i n e d with n o r a d r e n a l i n e was observed. These data are in agreem e n t with those o f Camargo et al. [51, s h o w i n g the existence, w i t h i n the septal area adrenergic system, of an c~-adrenergic p a t h w a y w h i c h s t i m u l a t e s the e x c r e t i o n of s o d i u m a n d p o t a s s i u m and a ~-adrenergic p a t h w a y t h a t i n h i b i t s it. These effects were c o n f i r m e d w i t h the use of the specific s t i m u l a t i n g agonist o f the c~ and t3 adrenergic r e c e p t o r s ( M e t a r a m i n o l and l s o p r o t e r e n o l , respectively). l s o p r o t e r e n o l i n j e c t e d i n t o the LHA i n h i b i t s sodium and p o t a s s i u m e x c r e t i o n , while M e t a r a m i n o l s t i m u l a t e s it. Thus, it w o u l d seem t h a t the c~-adrenergic p a t h w a y s t i m u l a t e s e x c r e t i o n , while the l~-adrenergic one i n h i b i t s it. These results i n d i c a t e the possibility o f an i n t e r a c t i o n b e t w e e n the adrenergic p a t h w a y s of the septal area with those of the lateral h y p o t h a l a m i c area, because, as s h o w n in the work of Papez [211, MacLean [18] and N a u t a [ 2 1 ] , the h y p o t h a l a mus is a s t r u c t u r e c o n s t a n t l y i n f l u e n c e d by stimuli c o m i n g f r o m o t h e r s t r u c t u r e s , such as the cerebral c o r t e x , basal nuclei, h i p p o c a m p u s , a m y g d a l o i d c o m p l e x a n d septal area. The p e r m a n e n c e of n o r a d r e n a l i n e near the r e c e p t o r s d e p e n d s on its r e u p t a k e by the nerve endings t o w a r d s the granule, or o n its d e s t r u c t i o n by the specific e n z y m e s COMT and MAO. When an i n h i b i t o r of n o r a d r e n a l i n e r e u p t a k e ( l i d o c a i n e ) is a d m i n i s t e r e d [13, 15, 2 4 ] , an increase in the renal e l i m i n a t i o n of s o d i u m and p o t a s s i u m occurs; similar effects are o b t a i n e d w i t h nialamide, an i n h i b i t o r of m o n o a m i n e oxidase activity [2, 9, 141. In the e x p e r i m e n t s p e r f o r m e d to verify the possibility of synergism b e t w e e n e n d o g e n o u s and e x o g e n o u s n o r a d r e n a l i n e , a s u m m a t i o n of effects was o b t a i n e d . These results d e m o n -

LHA AND E L E C T R O L Y T E S E X C R E T I O N

149

strate t h a t w h e n n o r a d r e n a l i n e is allowed to r e m a i n for a longer time, or at higher c o n c e n t r a t i o n s at the level of the s y n a p t i c cleft, in c o n t a c t w i t h the r e c e p t o r s , a p o t e n t i a t i o n of the n a t r i u r e t i c and kaliuretic r e s p o n s e is o b t a i n e d as c o m p a r e d with the n o r m a l a c t i o n o f n o r a d r e n a l i n e . When the LHA is s t i m u l a t e d w i t h n o r a d r e n a l i n e , a r e d u c t i o n in urinary v o l u m e occurs, c o n c o m i t a n t with natriuresis. This r e d u c t i o n is very well d e f i n e d at the 2 0 - 4 0 min interval and disappears later, suggesting t h a t this r e s p o n s e is m e d i a t e d in part by the l i b e r a t i o n of ADH a n d / o r o x y t o c i n . However, w h e n Regitine was given prior to n o r a d r e n a l i n e s t i m u l a t i o n , a blocking o f the n a t r i u r e t i c r e s p o n s e o c c u r r e d with n o i n t e r f e r e n c e on the anti-diuretic response. In s u m m a r y , the p r e s e n t results allow us to c o n c l u d e t h a t in the lateral h y p o t h a l a m u s the adrenergic system is

involved in the regulatory m e c h a n i s m o f s o d i u m and p o t a s s i u m e x c r e t i o n , acting antagonistically t h r o u g h its (stimulating) and ~ (inhibiting) receptors. F u r t h e r investigations will be necessary for the s t u d y o f the possible m e c h a n i s m s involved in the m e d i a t i o n of these responses. ACKNOWLEDGEMENTS This work has been supported by grants from the FAPESP, Sao Paulo, Brasil. The authors greatly appreciate the technical help of Francisco de Assis Tirado, Marina Holanda, Janete Carnassa Ribeiro and Mario Soares de Abreu. The authors wish to acknowledge the assistance of Maria Aparecida Protti de Andrade and Tereza Dias Moreira in the preparation of the histological material.

REFERENCES 1. Andersson, B., M. Jobin and K. Olsson. A study of thirst and other effects of an increased sodium concentration in the third brain ventricle. Aeta physiol, scand. 69: 29-36, 1967. 2. Bertler, A. Effect of reserpine on the storage of catecbolamines in brain and other tissues. Acta physiol, scand. 5 1 : 7 5 83, 1961. 3. Blass, E. M. Evidence for basal forebrain thirst osmoreceptors in rats. Brain Res. 28: 69-76, 1974. 4. Blass, E. M. and A. N. Epstein. A lateral preoptic osmosensitive zone for thirst in the rat. J. cornp, physiol. Psychol. 76: 378-394, 1971. 5. Camargo, L. A. A., W. A. Saad, C. R. Silva-Netto, C. G. Gentil, J. Antunes-Rodrigues, and M. R. Covian. Effects of catecholamines injected into the septal area of the rat brain on natriuresis, kaliuresis and diuresis. Can. J. Physiol. Pharmac. 5 4 : 2 1 9 228, 1976. 6. Coimbra, T. M., W. A. Saad e J. Antunes-Rodrigues. Estimulagao colin~rgica do hipotfilamo e excregao de sddio. CiOnc. Cult. 23: 333, 1971. 7. Cort, J. H. Spontaneous salt intake in the rat following lesions in the posterior hypothalamus. Physiol. Bohemoslov. 12: 502-505, 1963. 8. Covian, M. R. Fisiologia del area septal. Aeta physiol, latinoam. 16" 119-152, 1966. 9. Crout, J. R., C. R. Creveling and S. Udenfriend. Norepinephrine metabolism in rat brain and heart. J. Pharmac. 132: 269-277, 1961. 10. De Groot, J. The rat hypothalamus in stereotaxic coordinates. J. eomp. Neurol. 113:389 400, 1959. 11. Dorn, J. B., N. Levine, G. Kaley and A. B. Rothballer. Natriuresis induced by injection of hypertonic saline into the third cerebral ventricle of dogs. Proe. Soc. exp. Biol. Med. 131: 240-242, 1969. 12. Ehrart, E. A. Modifica~ao simptes e rfipida do mdtodo de Pal-Weigert para a colora~ao das bainhas de mielina. Arquiv. Neuro-Psiquiat. 9 : 3 7 2 374, 1951. 13. Glowinski, J. and J. Axelrod. Inhibition of uptake of tritiated noradrenaline in the intact rat brains by imipramine and structurally related compounds. Nature (Lond.} 204" 1318 1319,1964.

14. Green, H. and B. W. Erickson. Effect of trans 2-phenylcyclopropylamine upon norepinephrine concentration and monoamine oxidase activity of rat brain. J. Pharmac. 129: 237--242, 1960. 15. lversen, L. L. Inhibition of noradrenaline uptake by drugs. J. Pharm. Pharrnac. 17" 62 64, 1965. 16. Keeler, R. Effect of hypothalamic lesions on renal excretion of sodium. Am. J. Physiol. 197: 847-849, 1959. 17. Keeler, R. Natriuresis after preoptic lesions in rats. Can. J. Physiol. Pharmac. SO: 561-567, 1972. 18. MacLean, P. D. New findings relevant to the evolution of psychosexual functions of the brain. J. Nerv. Ment. Dis. 135: 289-301, 1962. 19. Mouw, D. R. and A. J. Vander. Evidence for sodium brain receptors controlling renal sodium excretion and plasma renin activity. Am. J. Physiol. 219: 822-832, 1970. 20. Nauta, W. J. H. Central nervous organization and the endocrine motor system. In: Advances in Neuroendocrinology, edited by A. V. Nalbandow, Urbana: University of Illinois Press, 1963, pp. 5 - 2 1 . 21. Papez, J. W. A proposed mechanism of emotion. Archs Neurol. Psychiat. 38" 725 743, 1937. 22. Saad, W. A., L. A. A. Camargo, C. R. Silva-Netto, C. G. Gentil, J. Antunes-Rodrigues and M. R. Covian. Natriuresis, kaliuresis and diuresis in the rat following microinjections of carbachol into the septal area. Pharmac. Biochem. Behav. 3." 985 993, 1975. 23. Silva-Netto, C. R., W. A. Saad, L. A. A. Camargo, J. Antunes-Roduigues, and V. R. Covian. Cholinergic stimulation of the lateral hypothalamic area on sodium and potassium excretion. J. Physiol. (Paris), 72: 917-929, 1976. 24. Slangen, J. L. and N. E. Miller. Pharmacological tests for the function of hypothalamic norepinephrine in eating behavior. Physiol. Behav. 4: 543-552, 1969.