Oxytocin is a hormone produced in the hypothalamus that stimulates contractions of the uterus during childbirth and the mammary glands to produce milk during breastfeeding. It plays an important role in bonding between mothers and their children. There are four main methods used to test the potency of oxytocin in biological assays: by measuring its ability to decrease blood pressure in chickens, induce contractions in isolated rat uteri, increase milk ejection pressure in lactating rats, and elevate blood pressure through vasopressor activity in rats. Each method involves carefully preparing test animals, administering doses of both a standard and test oxytocin preparation, and recording and statistically analyzing the biological responses.

1. k. Jayalakshmi
D/o k. kristaiah

2. Oxytocin
Role Of Oxytocin
Oxytocin – Mechanism Of
Action
Biological Assay Of Oxytocin

3. Oxytocin
 Oxy – Rapid
Tocos- Labor
 Synthesized in both sexes, well recognized physiological effects
only in women.
 Cyclic Polypeptide hormone - from posterior pituitary gland.
 Pituitary gland consist posterior lobe which produce oxytocin
and diuretic hormone.
 Neurosecretary product mainly synthesize in the cell bodies of
paraventracular nuclear of the hypothalamus.

4. ROLE OF OXYTOCIN:
• Stimulate the contraction of the uterine smooth muscle &
memory gland.
• Oestrogen progesterone & prolactin – responsible for production
of milk by mammary gland but milk ejection require oxytocin.
• Facilitates the contraction of uterus.
 It is presented as a solid or solution in a solvent containing an
appropriate antimicrobial preservative such as 0.2% w/v of
chlorbutol.
 Animal species - 90 - 110% stated number of units of oxytocin
activity.
 Synthetic: Solid - NLT 560 units/mg Calculated with reference to
the peptide content & when liquid NLT 150 units/ml

5. Oxytocin – Mechanism of action
Neuropeptide made in hypothalamus that stimulates contractions that
expel the infant from uterus.
Responsible for milk letdown & triggered by the nipple stimulation of
suckling.
Called love & bonding hormone. It has a very special affect on mothering.
Psychologically, oxytocin promotes a feeling of well being and tranquility.
It enables the growing sense of love and attachment to the infant. The
more the infant suck the more oxytocin is produced.
In mothers it increases their attachment to their infant, promoting the
feeling of love, and makes her infant more valuable to her.
It also suppresses the fear that would normally cause her to back off from
threat.

6. Biological Assay Of Oxytocin:
Principle:
Potency is determined by comparing its activity
– Depression of BP
– Contraction of Uterus
– Milk Ejection Pressure
– Vasopressor activity
with standard preparation of oxytocin
Standard Preparation:
Consisting free dried synthetic oxytocin peptide with human
albumin citric acid (12.5 units)
Method-A (Depression Of The BP In Chicken)
Test Animals: Cockerel (young male chicken), 1.2 - 2.3 Kg,
Method-B (By Contraction Of The Rat Uterus)
Test animals: Female rat 120 – 200g
Method-C (Milk Ejection Pressure In Lactating Rat)
Test Animals: Lactating rat, 3-21 day after parturition, 300 g
Method-D Vasopressor activity
Test Animals: Male rat 300g

7. Method-A (Depression Of The BP In Chicken)
Test Animals: Cockerel (young male chicken), 1.2 - 2.3 Kg,
 Anaesthetized cock-prolonged & constant high B.P
 Expose gluteus primus muscle(thigh) & remove politeal artery &
crural vein.
 Cannulate the popliteal artery & record B.P response
 Cannulate the crural or brachial vein.
 Prepare standard solution with saline. Inject 0.1 - 0.5ml
 Inject 2 doses of standard solution into cannulate vein is record
B.P response
 Dose should cause decrease in B.P (reqd. dose between 20-
100mUnits)

8.  Interval between 2 injection, between 3-10mins depend on rate @ which
B.P return normal
 Dil. test preparation with saline so as to get same response as standard
 The ratio between standard & test should be equal
 If animal rapidly becomes insensitive to repeated injection the soln
another must used.
 Measure all responses are calculated result of the assay by std statistical
method.

9. Method-B (By Contraction Of The Rat Uterus)
Test animals: Female rat 120 – 200g
 Inject 100ug of oestradiol benzoate IM into female rat before the
assay
 Immediately before assay confirm by vaginal smear that rate in
oestrus or pre oestrus.
 Kill rat & suspend one horn of uterus in organ bath containing a
solution of following Nacl,Kcl,Cacl2, NaHco3, Na2Hpo4, NaH2po4,
Mgcl2, Dextrose
 Maintain the bath at temp at of 32 c
 Bath liquid required dose between 10-50 units/ml.
 Oxygenate solution with mix of 95% of O2, 5% of CO2 record -
contraction of muscle.

10.  Record contraction produces by addition of two dose of std. ppn (Reqd.
Dose 10 & 50munits/ml of bath liquid)
 when maximum contraction has been reached replace - bath liquid
by fresh solution.
 Dose should be added at regular interval[3-5minutes]
 Similarly record the contraction of test preparation as standard.
 Ratio between two dose of test & two dose of std should be equal.
This ratio kept constant through out the assay.
 Measure all response & calculate result of assay by standard
statistical method.

11. Method-C (Milk Ejection Pressure In Lactating Rat)
Test Animals: Lactating rat, 3-21 day after parturition, 300 g
 Separate from litter & 30-60 minutes later anaesthetize (IP
Pentobarbitone Na).
 Tie rat to an operating table, at 37º, by its hind legs leaving front
legs free.
 Cannulate trachea with a short PE tube of i.d. 2.5 mm in such a
manner so as to ensure a free airway; apply artificial respiration
only if necessary.
 Cannulate an external jugular or femoral vein with a PE tube of i.d.
0.4 mm filled with saline & closed with a pin.
 Shave the skin surrounding the inguinal and abdominal teats and
excise the tip of one teat, preferably the lower inguinal teat.

12.  Insert a PE tube of i.d. 0.3 mm & e.d. 0.6 mm, to a depth sufficient
to obtain appropriate measurement of pressure (3-10 mm depth),
into the primary teat duct which opens onto the cut surface and tie
firmly in place with a ligature.
 Connect this cannula with a suitable strain gauge transducer
(such as that used for recording arterial BP in rat) and fill with a
3.8% w/v of Na citrate /saline contain 50 Units of heparin Na/ ml
to prevent clotting of milk.
 After cannulation, inject 0.05 - 0.2 ml of this solution into teat
duct through transducer to clear milk from tip of the cannula.
(This procedure may be repeated during the assay should
obstruction arise from milk ejected into the cannula).
 Clamp the strain gauge so that a slight tension is applied to the
teat and its natural alignment is preserved and connect the gauge
to a potentiometric recorder adjusted to give full-scale deflection for
an increase in milk-ejection pressure of 5.3 kPa.

13.  Inject all solutions through the venous cannula using a 1-ml
syringe graduated in 0.01 ml and wash them in with 0.2 ml of
saline.
 Prepare a solution of Std. & Test Ppn in saline solution so that the
volume to be injected is between 0.1 - 0.4 ml. Choose two doses of
Std Ppn such that the increase in milk-ejection pressure is about
1.35 kPa for Lr dose and about 2.7 kPa for Hr dose.
 As an initial approximation, a lower dose of between 0.1 and 0.4
milli Unit and an upper dose of 1.5 to 2 times this amount may be
tried.
 Choose two doses of the Test Ppn with the same inter-dose ratio,
matching effects of doses of the Std Ppn as closely as possible.
 Inject four doses (2 doses of Std & 2 doses of Test) at intervals of 3-
5 minutes.

14.  2 doses of Std and 2 doses of test should be given according to
randomized block or a Latin square design & at least four
responses to each -recorded.
 Measure all responses & calculate result of the assay by std
statistical methods.
 Potency - 90% - 111%. Fiducial limits of error are 80% -
125%stated potency.

15. Method-D Vasopressor activity:
Test Animals: Male rat 300g
 NMT 0.5 Unit /20 Units of oxytocic activity - by biological assay for
vasopressor activity- comparing activity of Test & Standard
Preparation of arginine vasopressin Freeze-dried syn. arginine
vasopressin peptide acetate with human albumin & citric acid
(supplied in ampoules containing 8.20 Units)
 Inject slowly into tail vein of male albino rat weighing 300g -solution
of a suitable a- adrenoreceptor blocking agent, (10 ml/kg body
weight of solution prepared by dissolving 5 mg of phenoxy
benzamine HCl in 0.1 ml of ethanol (95%) , adding 0.05 ml of 1 M
HCl & dil to 5ml with saline .
 After 18 hours, anaesthetize rat - that will maintain -prolonged &
uniform BP.
 After 45-60 minutes, tie the rat on its back to the operating table by
its hind legs.
 Cannulate trachea with short PE of E.D. 2.5 mm & dissect carotid
artery ready for cannulation.

16.  Then cannulate the femoral vein close to the inguinal ligament.
 Retract the abdominal muscles to expose the inguinal ligament.
 Retract superficial pudendal vein to one side & dissect femoral vein
towards inguinal ligament from corresponding artery.
 When dissecting, a deep branch reaching femoral vein must be
found & tied off to prevent bleeding during cannulation.
 Tie a short PE cannula of E.D. about 1 mm into femoral vein by
two ligatures & join by a short piece of flexible tubing to a 1-ml
burette with an attached thistle funnel containing saline at about
37º.
 Firmly fix wet absorbent cotton swab to thigh so as to cover
incision and cannula. At this stage inject through venous cannula
200 Units of heparin, dissolved in saline /100 g of body weight

17.  Then tie in a carotid cannula of E.D. about 1 mm & connect by a
column of saline contain heparin with a pressure measuring device
such as Hg manometer of I.D. about 2-3 mm.
 central & peripheral nervous system including both vagus &
associated sympathetic nerves is left intact.
 No artificial respiration is necessary.
 No air is injected, inject all solutions through venous cannula by
means of a 1-ml syringe & wash in with 0.2 ml of saline from
burette.
 Dil extract of Std & Test Ppn with saline so that volume to be
injected is between 0.1 & 0.5 ml.

18.  Choose 2 doses of the Std Ppn such that the elevation of the BP is
about 4 kPa for Lr dose & about 7 kPa but always submaximal for
higher, ratio of low to high dose being determined by response &
usually being 3-5. As an initial approximation doses of 3 and 5 M
Units may be tried.
 Choose 2 doses of Test ppn with same inter-dose ratio, matching
effects of dose of Std Ppn. Inject doses at intervals of 10 - 15
minutes.
 2 doses of Std & 2 doses of Test Ppn should given in randomized
block / Latin square design & 4-5 responses to each recorded.
 Measure all responses & calculate result of the assay by Std
statistical methods.