Биологические науки/8.Физиология человека и животных

S.B.Semenenko, N.I.Voytkevich, V.V.Semenenko, N.Yu.Semenenko

Bukovinian State Medical University, Chernivtsi

SPECIFIC FEATURES OF CHRONORHYTHMIC CHANGES OF THE EXCRETORY RENAL FUNCTION UNDER CONDITIONS OF HYPOFUNCTION OF THE PINEAL GLAND

Summary. The work examines specific features of chronorhythmic changes of excretory renal function under conditions of pineal gland hypofunction. Epiphysial hypofucntion was found to cause disorders of circadian organization of the renal excretory function in comparison with the control group of animals.

Key words: circadian rhythm, kidneys, pineal body/epiphysis.

Biological rhythms are periodically repeated changes of the character and physiological processes and phenomena peculiar for biological systems on all the levels of their organization [1, p.45]. The universally accepted conception about circadian body system includes the following functional links as pineal body (PB)/epiphysis and suprachiasmatic nuclei [2, p. 21] considered as the main biorhythmic generator of the majority of the body functions [3, p. 93]. The kidneys are also characterized by an accurate temporal organization of their functions, but peculiarities of circadian organization and the mechanisms of biorhythmic regulation of the renal functions remain insufficiently learnt. The objective of our research is to examine peculiarities of chronorhythmic changes of the renal excretory functions in albino rats under conditions of PB hypofunction.

Experiments were conducted on 72 mature nonlinear albino male rats with the body weight of 0,15-0,18 kg. The animals were kept in vivarium under constant temperature and air humidity on the standard dietary intake. The control group (n=36) was kept under conditions of usual light regime (12.00C:12.00T) for 7 days. The examined group included animals (n=36) kept under conditions of continuous light regime (12.00C:00T) for 7 days. On the 8^th day the animals were subjected to 5% water loading heated to room temperature and excretory renal function under conditions of forced diuresis was examined.

The experiment was conducted with 4 hour interval within 24 hours. The concentration and excretion of potassium ions, creatinine, and protein, glomerular filtration rate, relative water absorption and endogenous creatinine were studied. The results were calculated statistically by “Cosinor-analysis” method as well as variation statistics parameter methods. The diagnostics of functional peculiarities was based on the analysis of characteristic changes of mesor, amplitude, acrophase and shape of circadian rhythm curve. Obtained individual chronograms for every animal were grouped by the principle of maximal acrophase identity, and the traversable mesor, amplitude and phase structure (by the time interval between acro- and bathyphase) for every chronogram group was calculated by “Cosinor-analysis” method.

Examinations in the control and experimental groups of animals at night were conducted at faint red light (2 lux) which practically does not influence upon epiphysial melatonin biosynthesis. All the stages of the experiment were conducted according to the requirements of the European Convention for the Protection of Animals.

Obtained experimental data were processed on personal computers by the program package EXCEL-2003 (Microsoft Corp., USA). The value of an average arithmetical sampling (x), its dispersion and average error (Sx) was calculated for all the indices. To find reliable difference of the results in the experimental and control groups Student coefficient (t) was detected, after that the probability of sampling differences (p) and confidence average interval by Student distribution tables were defined. The indices with p<0,05 were considered to be reliable.

Pronounced changes of the renal excretory functions were found in the animals under conditions of PB hypofunction.

Diuresis chronorhythm became of a two-phase structure loosing its sinusoid rhythm character. Acrophase shift from 4 p.m. to 4 a.m. (fig.1) was observed as compared with the indices of the intact animals.

Attention was drawn to a reliable decrease of both urination mesor consisting of 2,5±0,34 ml/2 hours and rhythm amplitude (about 11%) concerning the indices of animals with physiologic PB function.

Considerable changes of diuresis were caused by disorders of renal filtration ability. Glomerular filtration rate was reliably lowered in all the periods of the day. Chronorhythm of glomerular filtration rate became of a one-phase character with maximal value at 8 p.m. (fig. 2), and the mesor of rhythm was 57% lower than in the intact animals.

Such changes are caused by reduction of areliable water re-absorption during the whole period of examination. This index was lower than that of the animals with physiologic PB function. The animals with PB hypofunction developed a two-phase character of the basic level of water reliable re-absorption chronorythm as compared with the control chronograms. Acrophase period was found at 8 p.m. and bathyphase – at 4 p.m.

Low ultrafiltration level caused a reliable increase of creatinine concentration in the blood during the day in comparison with the control group of animals. Rhythm acrophase was found in the period from 4 a.m. to 8 a.m. with the following peak at 4 p.m., miniphase was registered about at 8 p.m. Such circadian changes characterized instability and tension of glomerular renal apparatus work.

Mesor and amplitude of endogenous creatinine concentration index were reliably lower concerning the control indices, and as a result, a considerable rhythm change of the day period with disorders of its phase structure was registered.

PB hypofunction resulted in a reliable decrease (22%) of potassium ions concentration in the urine and rhythm amplitude as compared with the control group. Architectonic rhythm was of a monotonous character with the maximal index at 4 a.m. An average daily level differed from the same one in the animals with physiologic PB function.

Fig.1. Chronorhythms of diuresis in rats (ml/2 hours) under conditions of epiphysial hypofunction.

Table

PB hypofunction influence upon mesor and rhythm amplitude of the renal excretory function in white rats ()

Index	Control		Animals kept under conditions of PB hypofunction
	Mesor	Amplitude %	Mesor	Amplitude %
Diuresis, мл/2 год	3,2±0,28	18,7±1,55	2,5±0,34	11,4±0,71 p<0,010
Calcium ions concentration in blood plasma, mmol/L	5,1±0,29	24,8±1,41	3,3±0,12 p<0,001	5,3±1,42 p<0,001
Calcium ions concentration in urine, mmol/L	15,9±0,62	35,4±1,31	8,1±0,81 p<0,017	22,4±1,21
Potassium ions excretion, mkmol/2 hours	201,2±2,72	49,9±2,35	137,8±1,12 p<0,001	43,1±1,81 p<0,045
Creatinine concentration in blood plasma, mkmol/L	49,8±1,38	19,9±2,11	55,4±2,62	13,4±0,61 p<0,024
Creatinine excretion, mkmol/2 hours	3,5±0,44	16,9±1,91	1,7±0,22 p<0,004	17,8±1,32
Glomerular filtration rate, mkl/min/100 g	623,5±2,24	22,0±1,52	269,7± 2,32 p<0,001	66,6±1,01 p<0,001
Relative water re-absorption, %	95,1±0,56	1,6±0,41	91,9±0,59 p<0,003	1,8±0,31
Endogenous creatinine concentration index, UN	24,6±1,81	40,7±1,01	13,2±0,92 p<0,003	21,1±1,92 p<0,001
Protein concentration in urine, g/L	0,1±0,01	23,8±1,91	0,1±0,01	26,5±1,63 p<0,001
Protein excretion, mg/2 hours	0,2±0,03	29,1±1,22	0,1±0,02 p<0,028	32,5±1,39
Protein excretion, mg/100mkl of glomerula filtrate	0,1±0,01	31,4±1,62	0,1±0,01	140,8±1,86 p<0,001

Note: p – probability of difference between the indices of the control and experimental animals; n-number of animals.

During the period of examination the dynamics of potassium ions excretion became of a one-phase structure. Mesor and amplitude of the rhythm were reliably less from the control group. Acrophase was observed at 4 a.m., bathyphase from 4 p.m. to 8 p.m.

Fig. 2. Chronorhythms of glomerular filtration rate (mkl/min) in rats with PB hypofunction

Increased level of protein excretion was found at 4 a.m., minimal level of the rhythm was at 8 a.m. in the animals kept under conditions of continuous lightening.

Thus, PB hypofunction resulted in considerable disorders of chronorhythmic organization of the renal excretory function as compared with the control group of animals. The main signs of the detected changes are:

· architechtonics of urination rhythm became two-phase in structure loosing sinusoidal rhythm character concerning chronograms of the control rats with decrease of its mesor and amplitude;

· ultrafiltration rate decreased reliably in all the periods of the experiment, and the rhythm amplitude increased three times;

· the daily rate and rhythm amplitude of potassium ions excretion decreased.

Further research is directed to find the role of PB hypofunction in circadian organization of acid-regulating renal function.

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